Throttle Body Cleaning Question

My 1990 AW4 4.0 XJ has a pretty low idle (500ish rpms). Today, while idling in a parking lot, I turned on my AC. I kept on the gas and brought the idle up to around 1k RPMS. About 5 or 6 minutes go by, and I take my foot off the pedal, and boom, the XJ dies. Fired right back up without problem. I held the idle w/ AC on around 1k rpms for a second time, then let off, and it died for a second time.

When I rev the engine, it will sometimes stumble on it's way back down, but it usually catches itself before it dies.

I figure it's time to give my throttle body a good cleaning. Going to take it off tomorrow, and scrub it thoroughly. I just want to make sure I am not going to run into anything unexpected.

Will I need to readjust my TPS sensor? Or can I just take it off the TB, put it back on, and still be golden? If not, how does one adjust the TPS, and what do I need to do it?

Anything else I should do while I have the TB out? Anything I need to be careful of?

Also, should my EGR valve be replaced? I have 169k miles, and don't know if it's been replaced before or not. I've heard it's a pretty common cause of low idle on Renix XJs.

Thanks

if you take the throttle body try to clean the egr port from inside the intake as best as possible. there is no need to replace it if is not malfunctioning. as far as the throttle body, itself, remove the iac motor and clean the housing for that as well as the throttle plate opening. when you reinstall the t-body, remove the little aluminum plug from the side and back that screw out while the engine is running until it is almost flush with the side of the t-body housing, or 1000 rpm's. if you cant achieve 1000 rpm's at idle then you have to adjust the set screw where the throttle linkage bottoms out at the rear of the t-body. once you get it to 950-1000 rpm's then set your tps to 12-14%. that is the proper way to set the t-body up for optimum base idle and tps performance. after removing the plug on the side and adjusting the idle, you must aply a bit of rtv on the t-body so that screw cannot back out on its own.

jneary said:

if you take the throttle body try to clean the egr port from inside the intake as best as possible. there is no need to replace it if is not malfunctioning. as far as the throttle body, itself, remove the iac motor and clean the housing for that as well as the throttle plate opening. when you reinstall the t-body, remove the little aluminum plug from the side and back that screw out while the engine is running until it is almost flush with the side of the t-body housing, or 1000 rpm's. if you cant achieve 1000 rpm's at idle then you have to adjust the set screw where the throttle linkage bottoms out at the rear of the t-body. once you get it to 950-1000 rpm's then set your tps to 12-14%. that is the proper way to set the t-body up for optimum base idle and tps performance. after removing the plug on the side and adjusting the idle, you must aply a bit of rtv on the t-body so that screw cannot back out on its own.

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Thanks jneary. I had no idea about adjusting the screws. Done a lot of searching, and this is the first mention of them I see. But then again I searched for "throttle body" not "low idle."

Anyway, what will I need to adjust the TPS, and how is it done?

i adjust it with a scan tool. but if you do a search you can do it by reference voltage at the tps.if thats too confusing try an auto zone scanner or if all else fails, take it to the dealer.

What type of scanner do you use to adjust the TPS? I've got the info on adjusting it at the TPS, but was looking at other options. Mine's an '88.

i use the jeep scan tool at work. but the threads on this site work well. just remember the proper % is 12-14, no matter what the post say. the procedures are correct though.

Ummm, can I just take it to Shucks and tell them what to adjust it to? Will it be driveable unadjusted?

if you dont remove the tps, it shouldnt be out of adjustment by much after the cleaning, so it will be driveable. good luck and im interested to hear your results.

I just payed the local dealer 113 bucks to adjust my tps but Im needing to do the same thing as 90Pioneer. If I get the bolts that hold the TPS on nice and tight it shouldnt come out of alignment much right?

The biggest thing that kills tps's is water or carb cleaner. It gets inside and its all over, so be carefull.

Ill probably somehow block the tps so I dont accidentally shoot something into it. Thanks for the warning though.

I'm just about to start the taking it a part. I called Schucks and they said they would not adjust my TPS.

How can I do it, and what do I need?

The procedure has been posted here a number of times- try a search for TPS adjustment. Or, I copied this:
Adjusting TPS lessons
I have a 88 XJ and in the past year or so I replaced my TPS. I got out the instructions and set the feed back ratio to 83% like the book says. I took it into the dealer for a problem, the mechanic ran it on the test set and found a failed EGR. He also told me my TPS was out of adjustment and he put it back to spec for me.

I noticed the "at home" method has you use the transmission connector. The dealer method uses the engine connector since it is hooked up to the engine computer. The value at idle is 13% measuring on the engine connector.

I have heard on here that you need to use the Jeep/Eagle test set OR the snap-on MT2500. I have been looking at Ebay and finally bid on a used snap on unit. I had it deliver on Friday and over the weekend have been using it.

I used it on my 88 XJ and it only gives me current values, like everyone said, since the Renix has no memory. I then tried it on a buddies 88 oldsmobile with the buick 3800 V6. We did the TPS check and found he had a low value BUT no error code had set. He had installed a new TPS and used the multimeter method. So we adjusted his back into range.

I then took the unit to my cousin's and tried it on his 85 vette. We also did the TPS check and found he was out of range, he was also low. He had installed a new TPS using the multimeter method. We found this after our first drive - nothing like a 123 mph test drive We then set the TPS to the correct value using the snap-on tool then went for a second drive. He noticed it had more seat of the pants power but it solved his idle problem. He was sold just on getting a better idle.

We talked and concluded the multimeter method does NOT take in account any voltage drop in the vehicle harness. Using the test set you can find out what value the engine computer is using.

My thoughts are us renix XJ owners need to use the test set to calibrate the TPS, the multimeter is better than nothing but it appears the snap on tool is the way to go.

I did look a while and concluded I better buy a snap on scanner that said it had a "GM-FORD-CHRYSLER-JEEP" catridge. Some of the scanners had 93 cartridge but it only listed GM-FORD-Chrysler" so I was not sure. Also if you look on ebay make sure it has the Jeep-1 connector included for your renix XJ.
Sorry I missed the author's name- he deserves the credit for a good post!

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