Speed sensor cause this?

[LantanaTX]

I did some searching and was wondering if a bad/weak speed sensor could cause, inconsistent idle down when at a stop, no cruise control and inconsistent opening of the secondaries?

When I come to a stop the engine most of the time remains at a high idle but usually finally drops while sitting at a stop light.

secondaries don't seem to always be opening. I have good vacuum.

cruise control doesn't do anything at all. fuse is good.

does the speed sensor throw a code?

What code reader do you recommend? any OBD-1 work? If I use the paperclip method. is the flashing in the LCD disaplay or the check engine light. I also need to figure out why my check engine light does not work. Could it have been disabled somehow? When I turn the key to the on position it does not light up on the information panel.

Thanks for the help guys!

[tpr60]

High Idle in a 90 is common, GM did a updated prom to take care of this problem. I use this prom in one of my Zs and it works most of the time. Speed sensor if not working will set a code. Looks like someone removed the check eng. light bulb/or its burnt out. The light should come on when you turn the Ign. on as a bulb/circuit test, then turn off. You will not be able to do code test with a paper clip until you fix the bulb. I use a Snap-on scanner or most members use a Tech-1.

[LantanaTX]

High Idle in a 90 is common, GM did a updated prom to take care of this problem. I use this prom in one of my Zs and it works most of the time. Speed sensor if not working will set a code. Looks like someone removed the check eng. light bulb/or its burnt out. The light should come on when you turn the Ign. on as a bulb/circuit test, then turn off. You will not be able to do code test with a paper clip until you fix the bulb. I use a Snap-on scanner or most members use a Tech-1.

I have a 1991 not '90. ECM says remanufactured by GM on it. Should I look at the prom and get a number off it?

[tpr60]

First things first. Need to fix check engine light so you can pull codes with a paper clip, or borrow/buy a scanner. Either way the light fix is a starting point. Buying a factory service manual set is very important. Be careful removing the upper and lower trim around the radio/shifter to get to the check eng. bulb display.

[LantanaTX]

First things first. Need to fix check engine light so you can pull codes with a paper clip, or borrow/buy a scanner. Either way the light fix is a starting point. Buying a factory service manual set is very important. Be careful removing the upper and lower trim around the radio/shifter to get to the check eng. bulb display.

Thanks, will check bulb. I do have the 1991 FSM as well as the ZR1 supplement.

[tpr60]

Did the CEL ever work since you owned the car??

[LantanaTX]

Did the CEL ever work since you owned the car??

No but only owned for two weeks. I did have to have it inspected which included the sniffer and it passed.

[mike100]

The BFXB prom code is the latest for the 91 MY which included the idle and hot-start fixes. That said, the LT5 still cranks longer when warm and definitely has what some refer to as 'idle hang'. It idles up until you go below about 4 mph then finally drops to around 800 or so.

I have found that lowering the idle target speed at warmed up coolant temps helps this a little. Also may of these engines have a little bit of a throttle body leak or maybe another vacuum leak that kind of exasperates the ecm's ability to reach the desired idle speed. that can be checked by monitoring the IAC counts if you have a scanner or tech1. In my case, I custom made a PCV vent bypass to offset some amount of air going back to the plenum helping offset the throttle body wear leak.

[mike100]

Nobody really can say why the idle scheme is so complex and why the idle hang exists, but one of my theories is that the heavy engine and wider front tires needed more power steering pressure.

[LantanaTX]

Nobody really can say why the idle scheme is so complex and why the idle hang exists, but one of my theories is that the heavy engine and wider front tires needed more power steering pressure.
Thanks for the input. Just for grins, I looked at the prom. Looks like FXFK. someone wrote "91 Production LT5" on the side of it where it plugs in with a sharpie.

Sometimes it is a few seconds after coming to a dead stop that the idle works it way down.

[tpr60]

A good smog tech in Calif. would of caught the no CEL and not passed the visual inspection test. Don't know how it is in Texas. If you find the bulb is good its time to follow the trouble tree in the FSM, I believe its in section 8a index.

[PhillipsLT5]

I did some searching and was wondering if a bad/weak speed sensor could cause, inconsistent idle down when at a stop, no cruise control and inconsistent opening of the secondaries?

When I come to a stop the engine most of the time remains at a high idle but usually finally drops while sitting at a stop light.

secondaries don't seem to always be opening. I have good vacuum.

cruise control doesn't do anything at all. fuse is good.

does the speed sensor throw a code?

What code reader do you recommend? any OBD-1 work? If I use the paperclip method. is the flashing in the LCD disaplay or the check engine light. I also need to figure out why my check engine light does not work. Could it have been disabled somehow? When I turn the key to the on position it does not light up on the information panel.

Thanks for the help guys!
Do not know about secondaries as they are gone but no cruise control & idle issue, yep speed sensor shot

[LantanaTX]

Do not know about secondaries as they are gone but no cruise control & idle issue, yep speed sensor shot

Thanks, I read a thread where I think they found a faulty speed sensor, screwed up idle, stopped the cruise and secondaries from working. I will get on the check engine light fix. The smog tech didn't catch it thankfully! Since they didn't move the car during the smog test, the speed sensor works great when not moving! They did drive it around the building to check brakes etc. This is probably the first thread where no check engine light is a problem!

[PhillipsLT5]

Bill B was laughing that I blew speed sensor at Mojave 1.5 mile, I went too fast for it to handle LOL

[GOLDCYLON]

Bill B was laughing that I blew speed sensor at Mojave 1.5 mile, I went too fast for it to handle LOL


Well once you went past 88 Miles per hr there. :dancing

http://www.youtube.com/watch?v=k0kswK2aI08

[PhillipsLT5]

Thats a good 1, it was the 181.3 MPH pass, Bill & Greg loved it that that blew it out, I went too fast for it to handle, Life begins at 180 except for speed sensor

[LantanaTX]

Thats a good 1, it was the 181.3 MPH pass, Bill & Greg loved it that that blew it out, I went too fast for it to handle, Life begins at 180 except for speed sensor

That is pretty FUNNY. If you are going to blow something at 181mph, best to be the speed sensor!

Update: Been working on the car this afternoon and found some bulbs had been removed. Luckily the missing bulbs were sitting below the information panel behind the bezel. I used a flash light to see which of empty holes had something to display and needed a bulb. The check engine light now works as well as the service suspension light. The weird thing now is that the suspension now adjusts! finally a good firm ride.

The check engine light stays on but now I can get the codes. The low coolant light is also on but not low on coolant.

As soon as I started driving it the check suspension light went out and adjusted properly.

There is one more light on but my bad eyes had a hard time reading it. Looked like NFL RIEST??? What does this mean? I don't have an owners manual and my FSM is missing the first few pages (table of contents) and the last few pages of the index. Makes looking things up really challenging!

[tpr60]

INFL REIST is the air bag system not working. I think, if I remember correct that some systems will not function if that light shows a code,[ie: cruise control]. 90's had a service builetin about bad frame grounds at the sensors, think 91's had a updated system. Try disconnecting the ground side of the battery for 15+ seconds to clear some codes. See what comes back as a hard code. Then use the trouble tree for that code to attempt a repair.

[Racinfan83]

Correct me if I'm wrong - but I'm thinkin Marc told me another cause of high idle is a clogged MAP sensor hose? As in if there is a sag or low spot in the hose the oil can collect there and block it? I know he changed the one on mine and told me that was an issue with these cars...
I CAN tell you that mine idled way high and slowly worked it's way down when you stopped at a light before I had Marc work on it. He changed injectors, coils, MAP hose, fixed one of the secondary actuators, and fixed a few vac hoses. I also had him put his chip in it... Idles like a champ now!

[LantanaTX]

I pulled the stored codes and Have:

14 and 66

Is this coolant low and a/c low pressure?

My low coolant light is on (Will have to check wiring and sensor) and my a/c system is empty but will convert to R134 as soon as I locate the orifice and replace with a variable orifice.

Also would like to get that INFL REIST light off.

[tpr60]

My FSM is on loan right now so I can't reference it for codes. A/C codes are NOT available using the ALDL connector with a paper clip. You pull codes using the buttons on the A/C face plate above the radio, see the FSM on the procedure on which button to hold and puch. 09 code there is low Freon.

Codes 14 and 66 are ECM codes, refer to Emission section book for trouble code trees.
I found that most of the time the low coolant problem is a bad switch if the level is OK.

[LantanaTX]

My FSM is on loan right now so I can't reference it for codes. A/C codes are NOT available using the ALDL connector with a paper clip. You pull codes using the buttons on the A/C face plate above the radio, see the FSM on the procedure on which button to hold and puch. 09 code there is low Freon.

Codes 14 and 66 are ECM codes, refer to Emission section book for trouble code trees.
I found that most of the time the low coolant problem is a bad switch if the level is OK.

Thanks,

Here is the code list I found online which showed 66 as A/C. Thought it made sense since I have no Freon in the system. and 14 made sense since the low coolant level light is on as well.

If someone has better information on code 14 and 66, please chime in, Thank you.

[WVZR-1]

Thanks,

Here is the code list I found online which showed 66 as A/C. Thought it made sense since I have no Freon in the system. and 14 made sense since the low coolant level light is on as well.

If someone has better information on code 14 and 66, please chime in, Thank you.

14 - high temp coolant indicated

This is a pretty complete list all in one place with also the procedures to check everything using the controls in the car:

http://tech.corvettecentral.com/2011/01/c4-diagnostic-trouble-codes/

I maybe should mention ECM and CCM. I'm not familiar with a 66 for a '91. 66 for a '92+

Here's a link that displays codes by year and engine code '91/5.7J should be easily found. Rather than just point you towards the '91 I just posted the entire library:

http://www.troublecodes.net/gm/

[LantanaTX]

14 - high temp coolant indicated

This is a pretty complete list all in one place with also the procedures to check everything using the controls in the car:

http://tech.corvettecentral.com/2011/01/c4-diagnostic-trouble-codes/

I maybe should mention ECM and CCM.

Thank you,

Using the paperclip to jump the up two right pins, I got 14 and 66. On the list you sent via the link above, the only 66 I am seeing is DTC 66, A/C sensor, but that is '92 up and I have a '91.

[WVZR-1]

Thank you,

Using the paperclip to jump the up two right pins, I got 14 and 66. On the list you sent via the link above, the only 66 I am seeing is DTC 66, A/C sensor, but that is '92 up and I have a '91.

I added a second link and it agrees with the no 66 for a '91. I don't believe the FSM shows one either but MAYBE it's an FSM error. I certainly don't know! I believe I've seen 66 for a valet switch error posted previously. I would look further in that area I believe. Is your valet bypassed or non operational?

Here's a 10 year old post mentioning 66 for a '91 that was never responded to:

http://forums.corvetteforum.com/1547978885-post1.html

Here's where I recalled seeing it elsewhere and the bookmark was on a very old desktop:

http://teamzr1.com/ecmcode.html

Here's a post also from two weeks ago mentioning 66 on a '91 with no responses to the 66 code:

http://www.zr1.net/forum/showpost.php?p=199703&postcount=26

[LantanaTX]

Thanks, the valet works fine. I did disconnect it yesterday when I took of the bezel off to get to he information panel and its missing lights. I turned the key on to check lights before putting it all back together. I will clear codes again and see what comes back.

[LantanaTX]

I cleared the codes and almost as soon as I started it the Check engine light came on. Code 14. Then I drove to a car show last night 80 miles round trip and pulled the codes again this morning. Still just code 14.

During the trip Idle didn't drop below a 1000 until I came to a complete stop. A couple of time it didn't drop until a few seconds after was stopped. Also noticed the secondaries were not opening. I have good vacuum and am still suspicious of the speed sensor.

[WVZR-1]

I cleared the codes and almost as soon as I started it the Check engine light came on. Code 14. Then I drove to a car show last night 80 miles round trip and pulled the codes again this morning. Still just code 14.

During the trip Idle didn't drop below a 1000 until I came to a complete stop. A couple of time it didn't drop until a few seconds after was stopped. Also noticed the secondaries were not opening. I have good vacuum and am still suspicious of the speed sensor.

Address the code 14 - CTS

Why do you keep mentioning VSS - does the speedometer work? If yes the VSS is considered to be functioning correctly.

The 66 code never returned so that's behind you!

[LantanaTX]

Address the code 14 - CTS

Why do you keep mentioning VSS - does the speedometer work? If yes the VSS is considered to be functioning correctly.

The 66 code never returned so that's behind you!

I mentioned the speed sensor because I read an old thread where that was keeping the secondaries from opening on someone's car. My speedometer is fine. Could code 14 stop secondary opening? What other things stop the secondaries from opening when linkage moves smoothly and vacumm is good?

[edram454]

I have a 1990 and I recently replaced the VSS (vehicle speed sensor.). That sensor can cause lots of problems. when mine went out, my car idled differently. It would not idle down under 1000 rpm at a stop light, the secondaries would not come on, I was throwing suspension codes and check engine lights, car ran a little rough and definitely losing power. Fortunately for you, the 1991 speed sensors are cheap and plentiful. It was easy to replace so it is worth the effort. My car idles at a 1000 rpm and when it comes to a complete stop will go under 1000 rpm to 800 or 900 rpm.

I didnt realize who much power I lost until I replaced it and now this car is a rocket again. My car has mods and it is a stock cube car but runs very strong 405 rwhp. The speed sensor for a 1990 if you can get it, is around 300.00. Your 1991 should be around 50 bucks. Good luck.

ed ramos #3028

[LantanaTX]

I have a 1990 and I recently replaced the VSS (vehicle speed sensor.). That sensor can cause lots of problems. when mine went out, my car idled differently. It would not idle down under 1000 rpm at a stop light, the secondaries would not come on, I was throwing suspension codes and check engine lights, car ran a little rough and definitely losing power. Fortunately for you, the 1991 speed sensors are cheap and plentiful. It was easy to replace so it is worth the effort. My car idles at a 1000 rpm and when it comes to a complete stop will go under 1000 rpm to 800 or 900 rpm.

I didnt realize who much power I lost until I replaced it and now this car is a rocket again. My car has mods and it is a stock cube car but runs very strong 405 rwhp. The speed sensor for a 1990 if you can get it, is around 300.00. Your 1991 should be around 50 bucks. Good luck.

ed ramos #3028

Thank you, Did your speedometer work normally? It was mentioned above that if the speedo works then this sensor is fine. My speedo works fine, but your other issues it caused seem to be the same as me.

[LantanaTX]

Here is what I found searching the site:

"well here is the whole story about the src light coming on. This whole thing was caused by a bad velocity speed sensor (vss). It is located on the drivers side of the transmission. the part has been obsolete for over 10 years for the 1990 zr1 so getting one was very difficult. I managed to buy two of them. If your vss goes out, it will throw the src suspension lights on after 3 starts... if you drive a little you will get an engine service light and you will see that your secondaries have been killed also. My car sounded good but it felt a little down on horsepower and the idle quality was a bit rougher.

If the vss is not working, the car thinks it is not moving and the ecm gets confused when you are stepping on the gas but the car thinks its not moving.. The ecm will not throw the appropriate timing or gas so the car has a rougher idle and the idle down is impossible. I thought it might be my newly rebuilt gauge cluster but when I replaced the vss sensor today the lights reset themselves and the secondaries started to work again. What a difference!! It feels like it did when I bought it. The sensor was not to difficult to remove but it was very well stuck. It took a while but it came out. It leaked very little oil. I think the transmission was over filled anyway when we checked the fluid on the transmission. Car feels great and putting up some good power numbers."

[edram454]

Thank you, Did your speedometer work normally? It was mentioned above that if the speedo works then this sensor is fine. My speedo works fine, but your other issues it caused seem to be the same as me.

to answer your question, my speedo did not work at all. Thats how I knew my vss was bad. If your speedo works then it is not the vss.

ed ramos #3028

[edram454]

Here is what I found searching the site:

"well here is the whole story about the src light coming on. This whole thing was caused by a bad velocity speed sensor (vss). It is located on the drivers side of the transmission. the part has been obsolete for over 10 years for the 1990 zr1 so getting one was very difficult. I managed to buy two of them. If your vss goes out, it will throw the src suspension lights on after 3 starts... if you drive a little you will get an engine service light and you will see that your secondaries have been killed also. My car sounded good but it felt a little down on horsepower and the idle quality was a bit rougher.

If the vss is not working, the car thinks it is not moving and the ecm gets confused when you are stepping on the gas but the car thinks its not moving.. The ecm will not throw the appropriate timing or gas so the car has a rougher idle and the idle down is impossible. I thought it might be my newly rebuilt gauge cluster but when I replaced the vss sensor today the lights reset themselves and the secondaries started to work again. What a difference!! It feels like it did when I bought it. The sensor was not to difficult to remove but it was very well stuck. It took a while but it came out. It leaked very little oil. I think the transmission was over filled anyway when we checked the fluid on the transmission. Car feels great and putting up some good power numbers."

This is my post after I repaired my problem caused by my vss sensor not working. Like I said earlier, my speedo did not work so the sensor was the culprit.