Should have left well enough alone but I got the idea to clean the throttle body today. It was filthy. Used the wrong stuff - carb cleaner. After cleaning I reconnected and car starts with rpms way way too high 1800!
Installed new TPS and will do IAC adjustment tomorrow. I am real new to this but somehow I don't think IAC is the problem. I am ready to get new IAC if necessary....it is an 89 L98. Any and all assistance is greatly appreciated! thanks!

 

It's probable that your cleaning of the TB is now letting in too much air and the IAC cannot extend far enough to throttle down air flow.

You can use the carb cleaner on the IAC to assure proper operation.

Clean both the pintel and the bore under the TB.

Then reset base idle and you should be ok.

 

I was thinking about the air flow increase ...especially since I also cut the screens off the MAF....knew I shouldn't have done that! It is stuck well over 1k rpms when I start the car cold. I will clean all again and per your suggestion the pintel. IAC looks original. I will replace it if need be. They are $50 bucks. Intake plenum is real dirty also...I am tempted to clean that but would rather get the car back on the road soon. Thanks!

 

I was thinking about the air flow increase ...especially since I also cut the screens off the MAF....knew I shouldn't have done that! It is stuck well over 1k rpms when I start the car cold. I will clean all again and per your suggestion the pintel. IAC looks original. I will replace it if need be. They are $50 bucks. Intake plenum is real dirty also...I am tempted to clean that but would rather get the car back on the road soon. Thanks!

 

Did someone adjust the throttle stop in an attempt to correct the dirty throttle bore/plate situation. If so you may just have to reset the idle stop adjustment.

 

I don't know. I have had the car for 3 weeks so it is possible. I don't have a torx wrench long enough to reach the idle set screw so I am off to Sears. The rear of the TB was black with gunk but I was under the impression a dirty TB would cause a high or rough idle because the flaps might not close all the way. Today I am going to try these things....look for any broken vac lines, replace the IAC and reset it, reclean the TB and blow it out with air.

 

Did you clean the TB by immersing it in carb cleaner? Did you remove the TPS and IAC firsthand? Those items may have been ruined. If you merely cleaned the IAC passages, as you should have, and positioned the IAC pintle, properly, you may just have to go through the IAC resetting process.

RACE ON!!!

 

A small enough Allen wrench will work on a torx head unless you're dealing with one that torqued really tightly.

In a pinch, I've use an Allen bit on torx head intake manifold and runner bolts without damaging the torx head on the bolt.

Lots of work arounds out there if you keep your thinking cap on.

Jake

 

I sprayed the TB and cleaned it with shop rags and a toothbrush...left the IAC and TPS on and probably ruined one or both. I won't do that again!!

I recleaned the TB using TB cleaner this time...it was still dirty, especially in the IAC ports. Got a new IAC and TPS. I went through the IAC resetting process and adjusted the idle set screw using a Dollar store screwdriver set that has a torx attachment. It fit perfectly. The IAC resetting process worked perfectly. I did not recalibrate the TPS.

Now for the good news: The car now runs much better than before. Idle is much smoother and better throttle response . Cost me about $90 in parts but the IAC and TPS were probably origininal. I discovered that the old owner had set the idle way way high probably tocompensate for the dirty throttle body and IAC. Although frustrating and a little costly this was a great learning experience. Thanks a lot for all the input !

 

Thanks for letting use know the out-come.

Don't know what year engine we're dealing with, but the ECM on some year engines control the TPS voltage automatically so no adjustment is necessary, but in other years it has to be set.

I believe up through 89, you have to set the TPS voltage. If you've got one of those and if it is out of range you'll get a SES code telling you so. So if you have one of the adjustable kinds and AREN'T getting a code and the car drives fine, you'e good-to-go.

Unless you just HAVE to know the setting, I wouldn't worry about it. Of course if you do want to check it, you'll need a digital volt meter; engine "off", key "on".

Jake

 

I hope you aren't using that screw for setting the idle speed. That screw is for setting the "minimum air" adjustment. The idle speed is programmed into your ECM and regulated by the IAC.

RACE ON!!!

 

I have an '89. I am not getting a code and it seems to run fine but I need to keep an eye on it until I can get it properly adjusted.

 

Below is the procedure I followed...hopefully it is right. I understand the screw had a plastic plug over it to keep anybody from messing with it. It is off the car so the previous owner messed with it...it seems to be ok although I noticed the idle creeping up today. Does anyone know what the proper idle speed should be for an '89 l98? It now hovers around 600 in park when warmed. Thanks!!

"Procedure
There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC). Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC.

You will also be playing with the diagnostic connector under the dash. Remove the cover (if it's still in place). Bend your paper clip into a "U" shape. You will be playing with the two top right hand terminals ("A" and "B") in the connector.

* First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug. It's located on the driver's side of the TB. Remove this plug if it's there.
* With the IAC connected and the ignition "OFF," stick the paper clip into the diagnostic connector from "A" to "B." This grounds the diagnostic lead.
* Turn the ignition to the "ON" position without starting the engine. Wait 30 seconds.
* Now, with the ignition still in the "ON" position, disconnect the IAC connector at the IAC.
* Remove the paper clip from the diagnostic connector.
* Start the engine and allow it to reach normal operating temperature. The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.
* If your car is an automatic, set the parking brake and put the transmission in "DRIVE." If your car is a manual, leave it in neutral.
* Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
* Shut off the engine and re-connect the IAC."

 

 

THEN, go back and verify or set the TPS.

If the protective cap hasn't been removed from the throttle stop screw, *I* would wait to pop the cap, until the need for adjustment is established. If it is missing, you know the setting has been "messed with". Why leave doubt for the future if you don't have to.

RACE ON!!!

 

Thanks! I had intended to recalibrate the TPS but I don't have the proper pair of jumpers for my multi meter. I was going to order them from mid america...otherwise I understand I would have to penetrate the insulation on the TPS wires to do it. Is there another method? My idle is fluctuating a little so it has to be done......thanks again.....guess I will have to pop another one after I do the TPS ha!

 

I doubt the TPS adjustment is the cause of the fluctuating idle, but the TPS adjustment needs to be set, in any case. I am not a fan of piercing insulation. You can back probe the connector with paper clips.

RACE ON!!!

 

Don't poke holes in wires unless there is ABSOLUTELY no other way. You'd then need to re-seal the puncture or you'll just be asking for trouble down the road.

Jake

 

Thanks. I will try it with the paper clip. I don't know what is causing the fluctuating idle. Sometimes it is not returning to low idle when I stop at the light....it will stop at about 900 rpms. If I put in neutral and rev a little it returns to lower idle 500-600 rpms in drive. Do you know what the "proper" idle speed is for a stock high milage L98? I could not find in the service manual.

I will let you know what happens after the try the paper cllip. Thanks again.

 

You can't find it, because, properly done, YOU can't set it. As I said in an earlier post, the idle speed is burned into your prom (ECM). The throttle stop screw is for setting the "minimum air" adjustment. Look in your book for the procedure for that adjustment.

The TB not returning to the stop (idle?) screw sounds like warn throttle shaft bores in the TB casting. You can try lubing the shaft where it enters the casting at both ends. This may help if it isn't worn too badly. The shaft turns in the pot metal casting and wears it out over time. There are companies that can bush and seal your TB, or you're looking at a replacement.

RACE ON!!!