HELP--1990 Irratic Idle TPI L98
 

:willy: I have a 1990 that has an irratic idle. It idles around 1200 rpm but if you kick the throttle once it will idle back down to normal. Every time you push the clutch in you have to kick it once to idle back down. I have cleaned the throttle plate to make sure there wasn't a carbon build up. Any help would be appreciated.
:bigearsOK--here it goes. I change the IAC and the TPS first. I posted here and the recommendations that came back pointed to the Throttle Body which seemed logical as the shaft on the original one was sloppy. I ordered a new throttle body and installed it. Same thing. The car started up and idled fine. When I take off it acts as though the throttle sticks. It will idle around 3000 until I either kick it hard once or if I shut the car off while driving it and restart it the idle goes back down. I pulled it back in the garage and it was idling at 2000 rpm. I put the car in neutral, shut it off, restarted it and the idle went back to 1000 rpm. It has to be something electronic as the moment I shut the car off and restart it, the idle is fine until I give it gas

idle
 

did you clean the idle air control unit, it is under the tb on my 90 i put a helper spring on it and it work great, might have to do that also. but clean iac first, also clean where iac goes into

Iac
 

Yeah, I put a new idle air control valve in it and it did not change it.

It sounds like maybe the TB blade isn't closing all the way if a flip of the pedal fixes it. To sort of confirm that, next time it idles high, pop the hood and manually rotate the TB blade closed by turning the external part the cable attaches to. If it drops the idle to normal, then your TB isn't closing properly. I don't know what the fix would be, but at least you'd have it narrowed down.

I'll try that. It seems to work fairly freely.

Did you ohm the injectors? I'd look there.

Nope haven't tried that one yet. Not quit sure how, suppose I better look into that one.

:iagree:

When you "pop the hood and manually rotate the TB blade closed by turning the external part the cable attaches to", leave the engine running. If that drops the idle down where it belongs, the problem is a worn TB. The steel throttle shaft turns directly in the pot metal casting of the TB, no bushings, and the holes (throttle shaft bores) in the TB wear. There are outfits that will bush and repair the old TB or else it's time to start over again with a new TB.

Since kicking the throttle, idles it back down, it can't be the IAC. As a temporary cure, you can try cleaning up where the shaft goes through the TB body and give it some lube.

RACE ON!!!

???

Yes you would. And your car has been down for how long, for an injector change? How would kicking down the gas pedal affect the idle speed if the injectors were a problem??? If the injectors were feeding either too much or too little, the idle speed would be reduced, not raised. The idle speed is all about air intake. A vacuum leak can raise the idle speed. To maintain a programmed idle speed your car doesn't have a IGC (Idle Gas Control) does it?

RACE ON!!!

It has an idle air control valve that I changed. Didn't seem to make a difference though. I think the throttle shaft idea is the best so far. When I pull up to a stop sign it idles high when I push the clutch in. One quick burp and it idles right back down. The neighbor kid thinks I'm trying to be cool.:cool:

They ALL have an IAC. None have an IGC. But blipping the throttle has no affect on the IAC, as I said above. Too bad you didn't post before you threw money at it.

RACE ON!!!

First of all my car is down becuase I work from 8am to 10pm typically. I also have two little kids that need attention, they are 4 and 8. Softball, communions every week for the next six Sundays,etc... the REASON it is down is because I do not dedicate endless hours in the garage. The total sum of hours is actually quite small, not that I feel the requirement to justify it to anyone here.

Second, the reason I suggest it is that the original injector change I did was a result of faulty injectors which manifested itself as an idle that would not settle in. When the gas was stepped on it didn't come back to idle correctly. AND, BTW, it wasn't me who diagnosed it or did the work. I had Corvettes of Westchester do it because I simply didn't have the time for personal reasons. My car would drop to 700 or so and bump up to 1200, then fluctuate. New injectors solved the problem.

John is correct, It could very well be the fuel injectors. But i'm going to give you an even crazier idea. Have the car scanned at an auto parts store, and see what the Coolant Temp Sensor is reading. When mine was bad, the car did the same thing yours is doing. I am not sure why, but when I changed it, the engine when back to idleing normally.

John, pay no attention to the person w/ no name, he just lives to pick fights.

Randy

CFI is a good guy. His advice is right on most of the time. It's his delivery. I spend more time talking about the car than working on it, which, is kinda pathetic.

I had the same problem.

Solution:
EGR valve was not setting properly. I removed it and all is right again. While I was at it, I replaced a few of the 2 decade old vacuum lines and boots. This was a couple weeks ago. Here's hoping it stays fixed.

A bad fuel injector will create either a lean or rich mixture, either of which will reduce the idle speed, nine times out of ten, and in neither case will blipping the throttle reduce the idle speed.



Why, is because if the ECM thinks the engine is cold, it will increase the idle to a "cold idle" speed. However, blipping the throttle won't reduce the idle speed.



An EGR valve that isn't seated at idle is a vacuum leak. Besides a faster idle speed the leak usually results in a poor idle quality. However, regardless of the idle quality, blipping the throttle won't seat the valve and reduce the idle speed.

RACE ON!!!

It did on my car.

Sounds like the throttle body to me, could also be the cable. :iagree: with CFI on this one, don't think injectors, IAC or CTS has any thing to do with it....normally tapping the throttle will not have an effect on those components.

set the TPS to .54

his 90 is a non-adjustable TPS, and usually is around .6+

As stated if the idle kicks down from bliping could be either cables or worn tb shaft/assembly causing sticking etc..