High Idle Problem TPS voltage test procedure

[hpbadger]

I don't have the manual and am unsure how to test for TPS voltage....not sure what pins to check with multimeter etc.

I have been experiencing a high idle 1000 at startup and 1500 at a stoplight. Changed out the IAC which was dirty. Checked for loose vaccum hoses...didn't find any, checked ECM connections all ok,..so now I am at the TPS. Thanks!

hpb

[tomtom72]

The easiest way to do TPS voltage is a scan tool. Next is get ya some sewing needles and back probe the wire at the connector, be careful that you don't stab the insulation but get the needles into the brass terminal ends of the wire inside the connector.

The first time I checked my TPS voltage I had some phone wire laying around and made small probes from that, about 2" long and used a small needle nosed pliars to insert it into the back of the connector. At idle TPS = .54 volts.

Did you go over to the netreg site and look up the PROM recalls & TSB's? Ther were a coupla of updates to address idle problems. The TSB's describe the symptoms and cures (new PROMs) by model year.

Tom
Oh, forgot I think Corvette Central or MidAmericaMotorWorks has hraness test kits that you can buy to use to back probe all the main connectors, TPS, IAC, IAT, Oil & H2O....ya know ya yank the connector and put their connector in and it is a "Y" deal with a place for ya to put the VOM probes and still have the sensor in the loop.

[hpbadger]

Originally Posted by tomtom72

The easiest way to do TPS voltage is a scan tool. Next is get ya some sewing needles and back probe the wire at the connector, be careful that you don't stab the insulation but get the needles into the brass terminal ends of the wire inside the connector.

The first time I checked my TPS voltage I had some phone wire laying around and made small probes from that, about 2" long and used a small needle nosed pliars to insert it into the back of the connector. At idle TPS = .54 volts.

Did you go over to the netreg site and look up the PROM recalls & TSB's? Ther were a coupla of updates to address idle problems. The TSB's describe the symptoms and cures (new PROMs) by model year.

Tom
Oh, forgot I think Corvette Central or MidAmericaMotorWorks has hraness test kits that you can buy to use to back probe all the main connectors, TPS, IAC, IAT, Oil & H2O....ya know ya yank the connector and put their connector in and it is a "Y" deal with a place for ya to put the VOM probes and still have the sensor in the loop.

Tom thanks very much for all the info I don't know where I would be without the help from folks like you on this forum!

hpb

[tomtom72]

Hey hpb you're welcome!

I have a 90 so I have the 90 FSM but if ya need anything looked up shout at me & I'll go lookie see what's in my FSM. We're all brothers o' the beast so we help each other....man you should read some of my old threads...talk about a noooob! I was so intimidated by the whole package that I was afraid to look at it too hard

If I remember right the TPS is a three wire affair, a 5v reference line(gray), ground line(black), and a signal line(dark blue) .46v to .6v, .54v is considered to be good.

I'm still only a third year apprentice but ya gotta love how these cars make ya feel when they are right!


Tom

[Aurora40]

I would think the high idle is more likely caused by a leak somewhere than by an improper TPS. But I could be wrong. I'm not sure how a high-reading TPS could actually cause the motor to run much faster since it needs air to do that.

Did you clean the throttle body when you replaced the IAC?

[hpbadger]

Originally Posted by Aurora40

I would think the high idle is more likely caused by a leak somewhere than by an improper TPS. But I could be wrong. I'm not sure how a high-reading TPS could actually cause the motor to run much faster since it needs air to do that.

Did you clean the throttle body when you replaced the IAC?

I haven't clened the throttle body other than spraying the IAC hole with cleaner like crazy when I replaced it.

I replaced the TPS....the original was set to .34 but it was probably good. Checked for vaccum leaks and could not find any.

Got a QDM1 fault YES on the scanner. Noticed a hard to reach throttle cable stop but I don't want to mess with it.

Wierd thing is the speedometer is always reading 60mph to 220mph.

New TPS set to .54 did not fix the problem. I drove for 1 hr and idle suddenly came back to about 650 where it is supposed to be but I expect it to be high again when I start engine today. Real mystery. Hope I don't have to change the ecm.

hpb

[bldavis11]

Originally Posted by hpbadger

I haven't clened the throttle body other than spraying the IAC hole with cleaner like crazy when I replaced it.

I replaced the TPS....the original was set to .34 but it was probably good. Checked for vaccum leaks and could not find any.

Got a QDM1 fault YES on the scanner. Noticed a hard to reach throttle cable stop but I don't want to mess with it.

Wierd thing is the speedometer is always reading 60mph to 220mph.

New TPS set to .54 did not fix the problem. I drove for 1 hr and idle suddenly came back to about 650 where it is supposed to be but I expect it to be high again when I start engine today. Real mystery. Hope I don't have to change the ecm.

hpb

I have nearly the same problem as you and spent the my entire 3 day weekend working towards solving it, though I changed a ton of other things as well.

My problem is a faulty PCV valve connector tubing. The paired PCVs connect into a piece of rubber tubing about 10" long that runs along the rear of the block. You'll see if when you find the PCV valves.

After taking the tubing off, I could see that there are a number of very very small tears that are likely the source of my vacuum leak. A replacement house made from silicone is available from White Racing Products.

I also removed the plenum to check for vac leaks, removed the coil packs and starter to clean out the crap down in the valley, then cleaned everything well. In hind side, I'm glad I did all of this as there were clearly some mouse/rat droppings by the starter and my little friends had clearly been eating at insulation to the starter!

Replace the PCV valve hose and you'll be set. Watch out though. That little hose is over $150! I also rewelded the braces that connect to the aluminum tubing which connects to either end of this PCV tubing. One was snapped off and I didn't want to even think about how much it would cost to buy it new.

[hpbadger]

Originally Posted by bldavis11

I have nearly the same problem as you and spent the my entire 3 day weekend working towards solving it, though I changed a ton of other things as well.

My problem is a faulty PCV valve connector tubing. The paired PCVs connect into a piece of rubber tubing about 10" long that runs along the rear of the block. You'll see if when you find the PCV valves.

After taking the tubing off, I could see that there are a number of very very small tears that are likely the source of my vacuum leak. A replacement house made from silicone is available from White Racing Products.

I also removed the plenum to check for vac leaks, removed the coil packs and starter to clean out the crap down in the valley, then cleaned everything well. In hind side, I'm glad I did all of this as there were clearly some mouse/rat droppings by the starter and my little friends had clearly been eating at insulation to the starter!

Replace the PCV valve hose and you'll be set. Watch out though. That little hose is over $150! I also rewelded the braces that connect to the aluminum tubing which connects to either end of this PCV tubing. One was snapped off and I didn't want to even think about how much it would cost to buy it new.

Thanks a lot..I will take a look back there and see if the tubing is faulty and report what it is.....also the QDM 1 fault I found out is for a Quad Driver Module.....not sure what it is so am researching....just know it is in the ECM.

hpb

Originally Posted by hpbadger

Noticed a hard to reach throttle cable stop but I don't want to mess with it.

Do not touch the throttle stop screw. These came preset and Mercury Marine never adjusted them either. If you do adjust it you are masking the real issue.

Originally Posted by Aurora40

I would think the high idle is more likely caused by a leak somewhere than by an improper TPS. But I could be wrong. I'm not sure how a high-reading TPS could actually cause the motor to run much faster since it needs air to do that.

TPS dictates air and fuel coming into the engine. The ECM sees the increase in voltage and says I need air/fuel. It will add fuel and if it's not getting enough air with what it is is thinking (primary bore slightly open) it will open the IAC more. Engine will now idle higher.