I replaced the throttlebody and IAC, adjusted min. idle. (w/ ESC wire disconnected) I had to really screw the set screw out to get it to stay running, is this normal? I have drilled out the mounting holes on the TPS and adjusted it to .54. Is this right, or should it be adjusted to .62 since it isn't supposed to be adjustable? I am still having some idle problems, sometimes when started cold it's too low, other times it's too high, not always though. I'm going to replace CTS since it's cheap and see if that helps.

 

Doesn't sound right to me. I would try a different method. With my scantool and the car in closed loop with the AC and everything else off, I get about 15-20 IAC counts. After that, I get the TPS to 0.54V

 

I have read that 90 TPS isn't adjustable, and it should be .62, so I didn't know if that's best. I'll try to hook up Tunerpro, but haven't had much luck linking it up.

 

0.54 to 0.56. If you go much beyond that, the ECM might think it is off idle mode.

 

Why don't you fill out your sig? That way we know where you are and what you are working with. That way, if you are nearby someone, we might be able to help you better.

 

I filled out the sig a long time ago and wondered why it didn't show up, now I found the box to check so it shows.
Thanks

 

I've always been under the impression that ECUs in cars with non-adjustable sensors "learn" the minimum and maximum values the sensors put out, and therefore adjusting them is not necessary.

 

Indeed, after '89 the L98 TPS was NOT adjustable; instead the ECM "learns" what is "idle" and what is "WOT".

When you set min idle the IAC cable should have been disconnected. That is:
-jumper ALDL pins A&B
-turn On the key
-what maybe 1/2-1 minute
-unplug the IAC cable
-start the engine and set idle to 450RPM
-turn the key Off and connect the IAC cable

 

That it does. However, I would think at at 0.62V it will not learn what the idle is. This is also based on my car which is a 91 and didn't "learn".

 

I'm not sure how you set the IAC since it has been eons since I did it that way. IIRC, that is a way. Like I mentioned, going by IAC count is another way and has worked

 

It is not the same as previous years, you do not adjust or need to adjust the tps on 90-91. The ecm will see whatever volts .6+ with throttle blade closed as 0% throttle angle.

 

 

That's kind of what I thought, I'll adjust it to .6 or .62. Can I change the throttle stop a little as long as the TPS is set after the change? Mine is almost screwed all the way out now.

 

yes, re-seting the min. air (reference to the above throttle stop) is fine and after you re-start the motor the ecm will then see that as 0%throttle angle regardless of how open or closed the blade is (remember to turn the car off and re-start the car after all min.air adjustments).


I use a tuning program and set to counts, the stock method works fine as well (following traditional method of IAC unplugged, etc.). If I understand you correctly, the screw being all the way out would mean throttle blade almost closed. If I look at mine after set-up the blade is slightly open.

 

I think that when you have a stock motor, the stock method is fine. After that, it might be better to set to the IAC Counts

 

By all the way out, I mean that the screw is almost fully clockwise, which means the blades are open quite a bit.

 

With any car, I wouldn't rely on what something looks like for Minimum Air - which means just that - a minimum amount of air passing through the butterfly to keep it running somewhere around 450 rpms with the IAC disabled. Get your TPS to .62. Disable the IAC and check how many rpms it's cranking. When done, plug the IAC back in and start it with the accelerator slightly depressed. Let it run for 10 seconds; off for 5 seconds; then restart and if it's working right, Actual Idle will be +/- 50 rpms from Targeted in Drive; +/- 100 rpms in Park/Neutral. Note Actual, turn it off and immediately restart. Restart should be higher than it's last Actual, but return to that # with a second or two.

If all the above checks out - something else is going on. Take a look at the Coolant Temp and Air Temp Signal and make sure both show about ambient when the engine has sat overnight. Start it up and see how the Coolant Temp Signal rises - it should be fairly linear until the thermostat opens; then drop back a couple of degrees, and then rise to the threshold for fan operation.

Check fueling for a Rich/Lean condition.

Check compression - especially #7 since it's a '90 - or just pull that plug and look for rust on the threads

 

Something is wrong. That is WAY WAY WAY too much

 

What is that number coming from? I can't find it in any manual

 

Memory - every non-adjustable I've worked with - from TBI's 4's to sequential injected 6's have had this spec (and amazingly, some of the newer electronic throttles - so the OEM's must really like that number). If the FSM for your Year says something else, then use it. The self learning procedure for this TPS has been described by other members. Generally, if the signal indicates the vehicle is accelerating or at a steady cruise, the IAC won't control idle and at best you will get a surge. The IAC also acts as a Dashpot for decel and opens further (allows more air in) for a quick restart. None of what you've described seems to be a failure of the IAC to control something - sometimes it's one thing - at others it's something else, but that indicates the IAC is trying to do something so the source of the problem seems to be "a garbage in/garbage out" deal and I doubt the source is the low TPS signal. I would get it right and verify Minimum Idle (really no reason for it to change from when you last did it) and with some data from scanning, you should be able to figure this out. And from rereading your original post, pay attention to the CTS signal - that acts as a choke - colder more fuel and air; warmer less. I know you plan a new CTS, but problems with this circuit are more frequently wiring and/or the ECM - something a new sensor isn't going to turn up.