high idle problem update

[geogolf]

posted a week back about a high idle problem i am having 1990 L98. idles around 1500 to 1800, now here is new update when you bring car to a stop the idle will go down, to where its suppose around 800 if i coast at 15 mph in netural idle is 1500/1800 stop car goes to normal. car is very hard to drive at slow speed because it will not idle down has anyone ever had this problem as in prev. post checked iac/tps/vacuum lines sprayed eyther everywhere could not get any change in rpm, help ps tb is not hanging up

 

[vette-dude]

Have you checked the throttle cable itself? Sometimes these feel free but hang up at certain points along their travel.

Randy

 

[geogolf]

randy i have checked everything if it would idle high all the time might be able to fix it just does not make sense that when you stop car it ldles down is there some type of sensor that could be prob.

 

[gmjunkie]

randy i have checked everything if it would idle high all the time might be able to fix it just does not make sense that when you stop car it ldles down is there some type of sensor that could be prob.

I would Replace Idel Air Controle valve (IAC) and Clean the Sheet out of throttle Body!! This usely fixes it for me!! junk!!

 

[vette-dude]

randy i have checked everything if it would idle high all the time might be able to fix it just does not make sense that when you stop car it ldles down is there some type of sensor that could be prob.

Can't answer that cause don't know for sure but 02 sensor could be part of the problem. However, I have had throttle cables act alot like the problem you are experiencing. Also might check your return spring that is mounted on the throttle body butterfly shaft, drivers side where the linkage/cable is attached. Could be broke or weak, doubtful but we are grasping at straws here. Did you use throttle body cleaner or Carb cleaner? (I am assuming you have cleaned the TB.) Carb cleaner sometimes will mess up the IAC and the O2 sensor, too caustic. Just another random thought.

Randy

 

[RWDsmoke]

Check your throttle position sensor. I had a problem with high idle and found a bad tps would sometimes let the canister purge valve open at idle.

 

[gmjunkie]

Check your throttle position sensor. I had a problem with high idle and found a bad tps would sometimes let the canister purge valve open at idle.

good point!!junk!!

 

[geogolf]

replaced iac tps was .58 set at .54 throttle spring does seem weak but not that bad, what stumped me is car will return to normal idle when you stop at red light/stop sign or when you start it. when you are moving and you put it in netural car should go to normal idle but it does not around 1500/1800 till you stop and then it does would speed sensor have anything to do with idle car is going to shop on thur. hope they can fix it thanks for your replys

 

[C4Tom]

It sounds like something is closing a vacuum leak when you hit the brakes???

Maybe a bad diaphram in the brake booster. Does the idle go high when you let off the brake?

Start it and put it in gear, watch idle, let off brake, watch idle. Touch the brake enough to cause vacuum assist to come on but not stop the car. What's the idle do?

The only other thing I can think of is maybe a vacuum leak at the vacuum modulator on the tranny. Does the 700R4 still use that?

 

[Hrtbeat1]

Does the idle change between Park and Drive? It should only change about 200 RPM at most.


It sounds like a Vaccuum problem to me also. Have you checked the vaccuum in Park, Drive, brakes ON, OFF? Be aware IAC is a vaccuum leak. If vaccuum checks good .... ~18 in Hg, steady ... BTDT club! .... ECM .... especially on the SD cars ('90-'91) It was like $90 in HI at the local NAPA ... with exchange ... totally fixed high idle though. If you swap ECM's be sure to pull your MEMCAL.

 

[max]

Hey , I have the same problem too . Just have no idea why is it high . When it's warm it's 1300 idle ...

 

[geogolf]

max i took my car to shop hope they can figure it out if they do i let you know what it is i am almost convinced that my ecm is bad

 

[rrubel]

Huh. My car started doing the same thing after its rebuild, even with a new ECM and custom chip (also with the old chip). No vac leaks, newly rebuilt TB. Might have to check IAC...

Identical symptoms - idles at 15-1800 while driving (ie, shifting) and after stopping it gradually drops down to 800 or so.
[RICHR]

 

[geogolf]

update on idle called shop they said idle screw was not set right they set everything to specs. picked up car idles around 700/800 drove 5 miles put it in netural 1500/1800 again got home would not idle down turned car off 10mins. later started idles fine i am going to change ecm as soon as i get one will keep you guys posted ps will calll shop this morning see what they say

 

[jsinga]

unplug the IAC then all you should get is curb idle set by the throttle stop screw. If you still have high idle you need to find the vaccum leak.

Then you can troubleshoot one or the other problems.

JS

 

[Rickman2k]

this was my idle problem

after checking the wires, connecters, all that stuff, my idle was still anywhere between 1500-1800. I swapped out the TPS for a second time today and as I was working the throttle I happened to notice the TPS arm wasn't coming back up, it was sticking up against the Throttle body. I took the TPS back off, turned on my bench grinder, and very gently ground the arm just a tad and put it back on. Now I had free movement and when I worked the throttle arm, the TPS was moving freely. Turned her on and the motor idles just under 1000 now, much better but still a little fast, would like it to be just under 900. :cool