I need help with a stumbling/idle problem

[pantera1683]

Okay, for the past month or so I have been having an intermittent problem with the Z stumbling while cruising. I first noticed it while driving at constant highway speed on a trip from Dallas to Houston. It would stumble or "hiccup" for a few seconds at a time as if it wasn't getting enough fuel. It did this for about 1/2 an hour and went away. I pulled the plenum and changed the alternator, coils and wires. I checked all the vacuum hoses and added zip ties to the connections. The hiccups would pop up very rarely after that.

On Vets day I got caught in a downpour and the stumbling came back, but this time it had a hard time accelerating from a stop. It struggled to accelerate until I stabbed the gas pedal, then it would accelerate normally. I pulled over and it shut off. It did start back up immediately after and seemed to work fine after. Yesterday, it was driving fine until I got a block from home, the stumble came back coming trying to accelerate from a stop and the idle went to 1200 rpm and kept rising to 2000 rpm.

Here is some background on the car. It is a 94 with 36k miles on it. It sat for several years before I purchased it earlier this year. I bought it with 33,5k miles and the PO only put 2k miles on it in the preceding 2 years. The fuel filter and plugs were all changed earlier this year.

Any ideas?

[sammy]

you might ck the sensor that on the rear of the manifold (map sensor )to see if the vacume connection is either full of oil or if it has just a rubber hose that connects it if the hose has gotten soft and is collapsing .also there is a map sensor right under the computor in the engine compartment thats partof the the secondary system . are you getting a ck engine light . do you have a scann tool to ck for codes . other things that could be causing it are your tps ,might have developed a flat spot . or the iac may have started to go south . does your secondary vac pump go on and stay shut off when you turn the key to on (but dont start it ) or does it cycle on every couple of seconds ????if it does you still have a vac leak.

[XfireZ51]

How does it idle? Any surge?

[pantera1683]

Idles smoothly, the MAP hose is new and clamped secure. The vac pump cycles every 5 seconds with key on engine off.

[XfireZ51]

Idles smoothly, the MAP hose is new and clamped secure. The vac pump cycles every 5 seconds with key on engine off.

Vacuum Leak. Check secondaries.

[Paul Workman]

Idles smoothly, the MAP hose is new and clamped secure. The vac pump cycles every 5 seconds with key on engine off.

Vacuum "leak" in the secondaries, as Dom said. However, it is not severe. Furthermore, the secondary system vacuum leak will NOT be the source of your stumbling.

Do you have a scanner? I swear...The ZR-1 should come with one as standard equipment: not that they're trouble prone, but these cars are rare and not many shops have even seen a ZR-1. I got a scanner on a close-out sale, but I'd pay twice as much if I had to if I had to replace it!

That said, I'm gonna take a WAG and zero in on the TPS too, as I have a little spot on mine that I never notice if I sweep past it quickly. But, dawdle on the throttle opening, and I get a quick little stumble. It's on my radar, but not a priority item...yet.

P.

[pantera1683]

I don't think the vacuum leak is the source of the stumbling either. The secondaries are working fine. I did clean the IAC as it was kind of "sooty" and the idle went back to normal.

I need to get a scanner any recommendations on which one to get and where to get one?

Also, what's the best way to check the TPS?

Thanks

[XfireZ51]

I don't think the vacuum leak is the source of the stumbling either. The secondaries are working fine. I did clean the IAC as it was kind of "sooty" and the idle went back to normal.

I need to get a scanner any recommendations on which one to get and where to get one?

Also, what's the best way to check the TPS?

Thanks

Not sure why the pump would continue cycling if there is no problem with secondary vacuum.

TPS reading is easily done with scan tool. Bit more difficult using DVM

[pantera1683]

Not sure why the pump would continue cycling if there is no problem with secondary vacuum.

TPS reading is easily done with scan tool. Bit more difficult using DVM


There is a leak, but from what I've read it's just a minor one and wouldn't cause my problems, but I will take your advice and narrow down the leak just in case.

[XfireZ51]

There is a leak, but from what I've read it's just a minor one and wouldn't cause my problems, but I will take your advice and narrow down the leak just in case.

IMO, no such thing as a "minor vacuum leak".

[pantera1683]

Okay, it's been a couple days since I cleaned the IAC valve and so far so good. It's idling normally and no more stumbling. I'm driving to Ft Worth from Houston tomorrow and will keep you guys updated.

[sammy]

to ck the tps use a analogue volt meter needle should have a nice smooth sweep to it . if it jerks then it got a flat spot

[pantera1683]

I just returned from my Ft Worth trip and things went well for the most part. It was smooth sailing both ways until I got back to Houston. I was trying to make it all the way home without having to refuel but the level got down to reserve so I refueled. As soon as I got back on the highway it stumbed. It did a couple more times and then everything was fine for the last 20 minutes to my house. Do you guys think it might be fuel related?

On a side note I stopped by the Amsoil store in Arlington and picked up a few cases of AMO 10w 40:-D

[sammy]

jmho but i dont let my tank get below 1/2 ever . the pumps need the fuel to keep them cool. owning a 20 yr old car there is bound to be tons of trash in the tank . i would definatly change the filter and see how it runs after that . j just remember nothing good can come from running the tank way low . but thats just my old guy way of thinkin .

[sammy]

plus in new braunfels is corey henderson one of the best lt5 guys around . he could figure out what the problem is in nothing flat.

[pantera1683]

jmho but i dont let my tank get below 1/2 ever . the pumps need the fuel to keep them cool. owning a 20 yr old car there is bound to be tons of trash in the tank . i would definatly change the filter and see how it runs after that . j just remember nothing good can come from running the tank way low . but thats just my old guy way of thinkin .

I've heard that before, but didn't know at what level is too low. I changed the filter when I first got the car as part of my routine maintenance and the old one looked fine. I think I will pull the pump and take a look see, just to make sure the strainers are clear and have some piece of mind.

I will also pull the IAC again to see if it's still clean.

[pantera1683]

plus in new braunfels is corey henderson one of the best lt5 guys around . he could figure out what the problem is in nothing flat.

That's true but I'm not to the point where I need to take it somewhere to get it fixed. One of the reasons I bought an old car is because I like to turn my own wrenches.

[Paul Workman]

I don't think the vacuum leak is the source of the stumbling either. The secondaries are working fine. I did clean the IAC as it was kind of "sooty" and the idle went back to normal.

I need to get a scanner any recommendations on which one to get and where to get one?

Also, what's the best way to check the TPS?

Thanks

There are several scanners out there; AutoXray, Snap-On, Craftsman, are readily available. Sometimes you'll see a Tech-I (perhaps the most comprehensive scanner) pop up on Ebay. Mine happens to be an AutoXray; the only one I'm familiar with (haven't felt the need for anything "better" or different). I paid around $125 for it and $75 more for the computer software that allow me to graph the results (as opposed to reading the raw data points). Some scanners now come with graphing capability on the scanner itself - which I would opt for if buying another scanner.

But, in the end, I can't remember how many little quirks I've been able to detect that would otherwise frustrate the snot outta me. My first Vette was a 95 LT1 car that would intermittently run crappy. The shop had it and drove it for a week with "no problem found". Harrumph...:mad: I bought the AutoXray, hooked it up and took the car for a drive with the scanner in data logging mode. Soon as I hit about 3000 rpm, the right side O2 would short and go to zero volts, indicating super lean. The ECM would react by doubling the injector dwell time, resulting in flooding the right side of the engine (hence the black smoke from one side of the engine). I changed the O2s, and that was that; just the first of several little glitches since on that car and on the Z as well that the scanner has been able to immediately point out. Well worth every penny, dem scanners are!

P.

[sammy]

the thing about corey is you can call him and he will allways try to guide you in the right direction . he is a special guy , just ask rick hipsher , who is in katy tx , he will tell ya about the type of person corey is . you can email him at his business henderson performance any ?you have and he will tell you what he thinks . also rick is very helpfull and knowledgeable as well is his growing band of zr1 buddies . i would change the fuel filter agin just to be safe ,they are cheap and except for the gas mess easy to do . i too love doing my own work but am allways thankfull for the help and knowledge of this forum as i know you are finding out . please allway feel free to pm me if you think i can help you in any way . have a great turkey day :dancing