DoubleADuster

Howdy,

Ive been working on trying to fix this problem for two weeks now and Ive searched other threads and answers and come up right where i started: My car will start but it wont idle i can give it gas to keep it running and it revs smoothly up but if i let my foot off the gas it dies. I replaced the head gaskets two months ago, got everything back together, it did this at first and i replaced the tps sensor which was bad and then the car ran fine. I have since then replaced the MAF sensor and the MAF relays checked the vacum and pvc hoses and cant find anything not right. I suspect it could be the idle air control valve but its $93 for a new one and i wanted to check with people on here to see if that was a good next step. Is there somehting simple that im missing?

any help is much appreciated, thanks.

~
Aaron

skibum2100

Hello Aaron,

You have replaced some of the parts that cause common problems, which is good. I think you need to hook up a scanner to look at what the computer is doing to try to keep the car running. A HUGE vacuum leak could be the cause of this but so too could leaking injectors, so it is important to get your hands on a scanner and then try to pin this down.

For instance, I had a similar loping / dying idle and I had to put a penny behind the throttle adjustment idle screw just to keep it running. It wound up being old leaking injectors that were richen-ing up the fuel to air ratio so much that the car wouldn't run at idle...the IAC could never supply enough air to allow combustion to continue, it had to have part throttle just to idle. I couldn't tell this without a scanner because the computer was maxed-out trying to lean-out the mixture (BLM), but the car was still puffing black smoke (ludicrously rich). A scanner is worth its weight in gold sometimes.

Hope this helps.

D.J.

hey there, my car just started doing the exact same thing last night. did you found out whats doing it yet?

stealthroc89

Retrieve the trouble codes, if there are any. Won't tell you exactly whats wrong, but it'll get you started in the right direction.

D.J.

there are none, i've cheaked already with a scanner. i'm just wondering if DuobleAduster has found what was causing his problem.

MrPink

iTrader: (6)

I would replace the IAC and set minimum air. That usually fixes this problem. If not, it might be your injectors or ECM.

$97 for an IAC? No. Got mine for $40 at carquest.

D.J.

Thanks again for all the suggestions. It turns out it was the fuel pump was toast. My father had one of these a while back ('92 T.A. Dark green. awsome car) and lost his fuel pump when going around a tight corner while low on gas and had warned me not to run these cars fuel tanks real low. Well thats what I was doing when mine went out. Should have listened to Dad LOL.

On both cars, they would start but not idle or continue running.
I hope this helps some of you out there.

Iroc-Z Tone

my car just started doing that today. it had been running fine for months now since i bought it. today i got home & parked it then i tried to leave an hour later & it wouldnt start! it wont even idle unless i press the gas pedal. if i keep my foot on it, it stays on & idles fine. no back fire or black smoke.

streetpro

did you lock in your tps sensor after you set it with a volt meter

Iroc-Z Tone

i took off my IAC valve & cleaned it since it was very dirty. my idle improved alot & i could keep my car on now. i adjusted the IAC & TPS & locked it in. my problem now is the vacuum hose located under the throttle body. when its connected it makes my idle surge between 500-700 but when i disconnect it my idle rises & stays at about 900 rpms

skibum2100

Sounds like the mixture is a little rich and your engine enjoys the extra air to burn. Try to reset the minimum idle speed and see if that will solve the loping / uneven idle.

here's the procedure:
jumper A & B on ALDL connector
key on
wait 30 seconds
disconnect IAC
start engine
adjust idle to 450-550 rpms (check underhood sticker for confirmation)
key off
reconnect IAC
adjust TPS to .54V
enjoy the new, pleasant idle

Hope this helps.

Iroc-Z Tone

I will try to do that on Friday when im home from work a lil earlier. the Iroc isnt my DD so i guess thats a good thing but I will get back to you with the results. Thanks

rgarcia63

The port underneath the TB doesn't require vacuum it produces vacuum during part throttle when there's very little vacuum to operate the EGR valve.
This is called Ported vacuum:
A port located right at the throttle plates, used for controlling various devices that must work in proportion to throttle plate opening, such as the EGR valve. "When the throttle plates are closed at idle, there is virtually no vacuum signal at this port." But as the throttle plates open during acceleration, they expose the slot to a progressively increasing amount of intake manifold vacuum.

Iroc-Z Tone

oh okay, thank you. Ive been inspecting all my vacuum lines & noticed that when i disconnect the thin vacuum line on the passenger side coming from the EGR valve that goes into the T under the TB my idle smooths out but goes up to about 1500 RPM. Could that possibly be that I need to replace my EGR valve because when connected my idle surges.

rgarcia63

The vacuum line under the TB doesn't go directly to the EGR valve it goes to the EGR solenoid first. If it is connected to the EGR valve you need to correct the vacuum routing to how it's on the diagram under the hood. If you don't have one, or the hood isn't the original look on Chevy Thunder for the correct diagram.

Iroc-Z Tone

thank you, thats exactly where my problem is at. the PO who did the swap never put the EGR solenoid on the car. my EGR solenoid plug is just hanging there

IroczFan

if its a bad vacum leak u will hear it sucking air more than anything