Idle gone

[max]

Hello ? What should I check ? Vette doesn't wanna hold the idle . before it was kinda high , 1400 rpm , but yesterday ,after driving 40 miles onna highway , it started to stall after taking foot of the gas . And when you start it you have to hold the gas for it to run . If it's IAC , what do I do to check it ?

 

[C4Tom]

I would check the Throttle Position Sensor first. Any codes?

 

[max]

How do I check TPS ? You mean voltage ?

 

[Vettefan87]

Yes, stick two paper clips in the top two wires on the sensor. It should be somewhat like mine, just turn the key to the on position, but dont start it, it sould be like .54 volts with the key on, and close to 5 WOT.

 

[max]

okay , I 'll try

 

[WhalePirot]

Any codes?

This could be key, also. Is the SES light on?

Also, check the recent posts here on exactly how to proceed. A few others are having issues like you are.

 

[SSTibet]

O2 sensors may be??? I am saying that because that was my problem a year ago when the car started idling very erratically (got rough & died). Replaced all 3 sensors, cleaned the EGR valve, got higher quality gas & the problem never ever showed up again. Rough idle did not happen when the engine was cold but after drining the car for some miles.

 

[max]

Well, checked the TPS yesterday and it is okay . 0.5 at closed throttle and 4.9 at WOT .
Checked the codes , all clean . only 32 , which is EGR . And that , as I ve been telling in some tread here , is because previous owner disconnected connector somewhere, so EGR does not operate now , so when you drive on a highway for some time SES comes on . But no new codes , it flashed 12 3 times and then 32 three times .
So if the elecronics okay , it may be pure mechanical problem ?
I opened throttle body to inspect it and it is pretty sludgey . K&N is not really dirty . Where did it come from ...
Guess for now it is IAC . Maybe stuck ? How do I check it ?
Thanks for posts , guys . Good to get some help from those who been there .

 

[C4Tom]

Checked the codes , all clean . only 32 , which is EGR . And that , as I ve been telling in some tread here , is because previous owner disconnected connector somewhere, so EGR does not operate now , so when you drive on a highway for some time SES comes on . But no new codes , it flashed 12 3 times and then 32 three times.

First reconnect the EGR. Not saying that's your problem, but don't leave a possible fault open. It could be causing the real culprit or hiding it.

So if the elecronics okay , it may be pure mechanical problem?

You could have a vacuum line that's disconnected somewhere. Slowly move your ear around the engine and listen for hissing.

I opened throttle body to inspect it and it is pretty sludgey . K&N is not really dirty . Where did it come from ...

I thought the throttle body was just an air valve. How could it have sludge in it? You might as well remove it and hit it with carb cleaner.

 

[Moonunit 451]

I'm kinda with Tom here. I bet it's a vacuum leak. If you claen the TB there is special TB cleaner, some say that carb cleaner can mess with some seals or something.

For checking for vacuum leaks many use cab cleaner spred toward specific suspect areas (anywhere a leak might occur). And some use propane in the same manner. If you get to a leak the RPM's will change, and you'll have found the problem area.

 

[WhalePirot]

I thought the throttle body was just an air valve. How could it have sludge in it?

It is, but if the air filter has too much oil applied to it, guess where it goes.

 

[MoeJr]

Check the Idle Air Control. My bet is it is stuck from being sludged up.

 

[C4Tom]

It is, but if the air filter has too much oil applied to it, guess where it goes.

AAahhhhh!

I was picturing my old quadrajets in the past with sludge in the bowls.

 

[max]

Whoa, thanks for replys Took off throttle body yesterday , it's full of some carbon like deposits and when I screwed IAC out, it was not a good picture . Sludgey . So today I gonna clean it and how to check it ? From the manual i read you gotta measure impendance between contacts A and B , and C and D
gara be between 40-80 ohms . But is there any way to check if it moves freely after clean up , I just do not have anything like IAC driver
Well , anyway I also dug in the manual yesterday and read that problem cause can be inna EGR valve . If it is open all the time then too much of exhaust gases enter the intake and thus poor perfomance and even stalling. And maybe that's why plenum so gas smelling and oily inside ?
But if the EGR solenoid disconected then it doesn't provide vacuum to EGR valve and valve is closed . --> high temps in combustion , overheating .. So I am in a doubts now

To Whalepirot : No the filter is kinda dry , no oil drippin'
To C4Tom : listen for hiss ? I could be in danger of becoming fried and deaf
All others : thanks thanks

 

[max]

Also , PCV valve could be the reason for rough idle and stalling ... I read . Big book that manual .

 

[Jeb]

How did it run after you cleaned the TB and IAC valve?

The EGR sensor pigtail is plugged in behind the distributor on my '87 and it's a real bear to connect with the distributor in place. If you have the L98, it can be done if you have patience and long dexterious fingers.

 

[C4Tom]

The EGR could be bad and maybe that's why previous owner disconnected it. Being bad, it could be sticking partially open or sticking closed.

A PCV valve is just a check-ball. Clean it and reinstall it. You shouldn't need a new one unless it's cracked/broken or you can't get it to rattle when you shake it.

 

[max]

Oku doku , me came today to work on a VETTE
Cleaned a lot of bad stuff out of throttle body yesterday , hand job all . Almost broke my fingers
Result is good Thanks all . I guess after all it was sticking IAC .
C4Tom : haven't reconnected the EGR yet , but I will try that . Idle is still 1400 -1100
maybe it is because of disconnected EGR , maybe because of IAC itself , I cleaned it outside , but who knows maybe it does not retract all the way out because of sludge inside it ??? ..
But car runs well now .just as it did before .
Also I guess throttle body had so much sludge ( dust and oil) in it maybe bacause the K&N lid was not tight enough ?? That engine is pretty "sucky " I figure .
Again thanks for help , everyone .
Now have to collect my acts together and get the chain changed .

 

[max]

Actually , some tuners here told me to ditch the EGR at all , saying that more power will be available . Interesting , how more ? The engine health kinda more important for me that 5+ horses .
Friend of mine made headers himself and naturally lost the EGR . But that was japanise turbo engine , durable as they are against heat in combustion chamber . What about L98 ?

 

[C4Tom]

Your high idle could be from a vacuum leak. Try spraying some carb cleaner around the TB while it is running. If the idle climbs even more, you have a leak somewhere.