High Idle When Car is warm

[vettin1]

Hi all!!!

I am having a problem that is turning my hair grey! :confused

I have an 85 w/a manual tranny. The car idles at about 1500 rpm when warm. The check engine light came on once reporting an EGR problem, so I spent a few days and a lot of bloody knuckles later, replacing the temp switch, EGR solenoid and diaphragm. NO LUCK. Still having the problem.

When the problem starts, almost all of the time I can get the car to fix itself by disconnecting or reconnecting the fuel vapor canister solenoid (a discontinued part). Could the solenoid or vapor canister be causing the problem???

Idle air control solenoid changed 2 weeks ago, EGR sys changed, TPS Sensor changed 1 year ago and no check engine light. Car drives fine on highway and when idling OK. Thats where I am now.

PLEASE HELP!!! Car sitting in driveway begging me to drive her!

Thanks for all the help in advance!

 

[WhalePirot]

I wonder if you have a vacuum leak. A vacuum gauge can help diagnose all sorts of problems. I would use it before getting further into this, as the ECM troubleshooting assumes the visual check is okay and that basic mechanical things are in order. Even if you don't already own one, you'll need it for the flow chart below.

There are: EGR solenoid and EGR temperature switch which feed the vacuum driven EGR valve.

I will e-mail you a digi-photo of the Chevy trouble shooting pages for Code 32 (EGR).

 

[EricVonHa]

I spent a ton of time trying to get an '85 to idle properly. As was mentioned directly before this you need to be sure that you've got good vacuum on the motor. There are numerous and crazy routings of vac line. Check your emissions sticker on the radiator housing for more detail. Then, after verifying the continuity of the vacuum system-- then you get back to setting the IAC. There's a very specific procedure for setting the IAC and TPS sensor. Sorry I don't have a link handy...however there is probably something archived on this site.

Also, check the timing of the motor after you get your vacuum stuff squared away. Chances are that if the problem has existed in a previous lifetime that someone probably monkied with the timing to compensate for the erratic idle.

 

[vettin1]

Thanks for all the suggestions.


I do have the GM '85 shop manual with all codes and the descriptions. I have replaced the entire EGR system as well as the IAC valave and PCV valve. I have set the idle speed and the TPS sensor to specs. It seems to run fine for a while then the idle starts to climb but it will fix itself for a bit when i drive on the highway, then start up again.

Could this problem be caused by the Vapor canister purge solenoid???

The timing I will check as well.

Vaccum also seems to be good with no leaks. While disassembling the plenum and all parts to replace EGR system, I was able to get a real good look at all vaccum lines and they all seem to be fine pulling a nice amount of vaccum.

Will keep everyone aprised of the progress.

 

[unknown1]

How warm is it getting?Is it enough that the ecm could be increasing the rpm to get coolant flow?

 

[vettin1]

normal operating temp 200-225 on the coolant and approx 195-215 on the oil temp. This is just when I'm idling her in the driveway seeing if she'll do it again.

 

[vettin1]

Increasing RPM to improve coolant flow I can understand but it's idling at 1100-1500, steady. I blip the gas and manually make sure the butterflies on the TB are closed all the way and it doesn't improve.

For all these reasons and the fact that when I drive it on NYC streets in traffic it starts right away, it leads me to the conclusion that it is electrical/computer.

I am ready to shoot the car with a shotgun ad and put her out of her misery or mine.

 

[WhalePirot]

Don't shoot anything, just yet.

I did not know that the ECM would adjust idle speed for coolant flow. I thought it turned on the fans, in later cars.

LOOKING at vacuum lines may or may not tell you anything. A decent vacuum gauge will. Finding a leak, if it is low, is quite fun. WD-40 sprayed on areas could point to it quickly, if the leak is accessible. Mine never are, but yours??

I would have to research the logic and function of the cannister solenoid et al., but it sounds like an area to explore.

 

[vettin1]

If it does turn out to be the vapor canister solenoid there is one problem with that, GM/ACDelco discontinued the part w/no replacement and I can't find an reproduction/aftermarket part made by anyone else. What does one do if this part ever goes bad??? Give the car to charity???

I know someone that has a vaccum pump etc. to diagnose, I will let you know what happens.

Thanks for all the help thus far.

 

[unknown1]

Please dont shoot anything(I have a list for you to use)!Looks like we have another part that needs to be reproduced? We have to be careful what we pull from the gene pool. Bear with me ,OK?

 

[WhalePirot]

Google yields a test starting point:

http://autorepair.about.com/cs/troubleshooting/l/aa042603a_09.htm

I doubt that the canister is specific to the Vette; another may work just fine, in fact, I think mine is a replacement, which looks nothing like te original; smaller by a LOT, but cannot look at it until I return to the US.

 

[vettin1]

The canister is easy to find, its the solenoid for the 85 I can't find.

Are you saying that I may be able to use a solenoid from another year that is still made?

I will be performing the vaccum test soon, I will post what I find.

 

[vettin1]

Finally Found The Problem

Well, it turns out that the whole problem was a bad TPS sensor. I noticed that I would configure the sensor, drive the car for a bit, it would start idling high again, so I tested it while the car was still running. It was throwing a .75-.80 and higher signal. I changed the sensor and my baby is back in operation. Never thought a TPS that was 1 year old would fail. We all know what happens when you assume :eyerole .

Thank you to everyone for the suggestions.

Now on to the next project (us vette people can't just leave our cars the way they are)!