Last night I decided to remove and clean the IAC because I had noticed an occasional surge in the idle (very slight but I like everything to be perfect). I cleaned the pintle and the spring with throttle body cleaner and reinstalled it. I started he car up and it idled around 1500 rpm. I shut the car off and went to adjust the idle. I set it at about 550 rpm following the procedure in my Haynes manual. I checked my TPS voltage and it had dropped down to .40 When I went to adjust it, I couldn't get it to go any higher than .48 because there was no more room for adjustment. There has to be something wrong with that picture. I ended up adjusting the idle screw so it would idle about 700 and the highest I could get the TPS was .50 I started the car up and drove around a bit and stopped at the gas station. When I started the car back up, it was idling real erradically and was trying to stall. I revved the motor a few times and that seemed to smooth it out. I was able to drive home. When I started it up again at home, the car stumbled for a couple seconds and then died. Tried it again 3 times and it did the same thing. I started it again and immediately revved it for a few seconds and the idle came back down around 800 and satyed there. I messed with the idle adjustments and TPS voltage a little more but with no luck so I went to bed. When i went to start the car this morning, it did the same thing. It would die almost immediately. If I revved it and held it at about 1000-1500 rpm for 10 seconds or so, it would drop back and idle fine. But once I turned the car off and started it again it would do the same thing. The computer is not throwing any codes and the car runs great other than that. I'm thinking I could've cooked the IAC somehow or maybe I just need to clean it better. When I get home, I will clean out the IAC passages in the throttle body really well and see if that helps. Any other suggestions? Would the low TPS voltage cause this? Sorry for the long post but I really need to get this fixed ASAP.

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1991 Z28 - 350 TPI, T56, McLeod street clutch, LT4 pressure plate, Pro 5.0 shifter, ported plenum & runners, AFPR, Hooker shorty headers w/o AIR, Flowmaster muffler, homeade ram-air, SSM subframe connectors, Kenny Brown STB, Global West steering box brace, Steve Spohn adjustable torque arm and T56 crossmember

 

You may just want to replace the IAC and TPS, I think your IAC is slowly failing and it's sluggish in responding but won't set a code.

 

As far as the TPS, the computer will do what is called AUTO ZEROING, meaning when it drops below 1 volt, the computer says, hey throttle is closed, zero value set.

 

That's exactly what I was thinking. The IAC isn't working at full potential. Correct me if I'm wrong but doesn't the computer allow 10 seconds for a sensor to correct itself before setting a code? I guess it is doing what you said and responding sluggishly.

And could you explain a little more about this "auto zeroing" and how I can fix the problem?

Thanks

 

Is there a special way to reinstall the IAC valve? I was reading through the archives some more and saw where someone said you have to push the pintle all the way in and then screw it back into the throttle body. Is this correct?

 

Correct me if I'm wrong, but isn't the TPS on your car not adjustable? (or not supposed to be adjusted)

Personally, I don't agree with taking the IAC apart... soaking it in WD-40 works just fine. However, I assume you took that damned thing apart. If you don't push the pintle all the way in (or most of the way in) you risk the pintle seating itself before you torque it down. Example:

As your turning it in, the pintle seats, but it's not torqued yet, so you keep turning it in (not your fault, you really can't tell) you keep turning it in, and the pintle gets forced back (not gently wobbled back in, like your supposed to), and therefore the worm gear gets nicely f'ed up.

Part of cleaning the IAC is cleaning to passages, go ahead and do that and see if it helps. Otherwise go ahead and buy a new IAC and TPS. Sorry it has to be that way.

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1985 Camaro SC - 2.8L, auto.

http://www.xenodrgn.f2s.com/Frontright.jpg

 

No, the TPS definitely is adjustable. And I didn't take the IAC apart, I just took it out of the throttle body and sprayed it with throttle body cleaner (or is that what you meant by taking it apart). As soon as the motor cools down some, I'm gonna go take the throttle body off and thouroughly clean the IAC passages. Just in case, I had the parts store order me a new IAC for tomorrow just in case this one's fried.

 

If the TPS is adjustable and youre not getting the value you need, your TPS may be hosed. Just a thought

Clayton

 

on my tbi car the iac is pulled all the way in when the car is not running and once you have used it once you can't adjust the pintle because you can damage the gears inside it.

 

Ok I fixed the problem. All I did was manually push the pintle all the way back into the housing and then installed it. I followed the standard procedure for resetting the IAC and it works fine now. The TPS is still slightly off. I cna only get it to read .51 volts and then it runs out of room for adjustment. Thanks for all the help.