arpunk

Which of his suggestions are you referring to?

I turned the TPS down to 15% - no change.
I sprayed for vacuum leaks - no change.
NAPA parts for MAP sensor finally arrived today.

Rogue4x4

Yeah, spraying for leaks and replacing that janky vacuum line

arpunk

Yup. All the usual suspects were sprayed. The entire vacuum harness was one of the first things I replaced. MAP-TB line/elbows/fitting arrived today. In my experience messing with that line drops RPMs violently but I’ll change it out regardless.

I’ll see what happens after I change out these injectors and go from there.

arpunk

Swapped out the injectors. Took two hours in the rain at 36 degrees.

I let it run for five minutes and the idle was steady at 750 so fingers crossed it was a vacuum leak where the injectors sit.

Update: nope! Still 1k. The hunt continues.

MJ/XJ Owner

The TPS on Renix fuel injection was very sensitive to moisture and water intrusion and or chemical cleaners, if you got it wet or sprayed cleaner on it you may have damaged it.. Biggest problem we had with high idle or idle racing was the TPS and bad connections or moisture. Never had problems with idle air motor.

arpunk

I can try a new one to rule it out.

When you adjusted your tps output were you seeing idle variations in real time? I can rotate it from .6 to .9 and it doesn’t seem to affect the idle. Output voltage changes with throttle position and appears to be functioning properly.

it’s an easy fix and free if it isn’t the problem so I’ll try a new one.

lawsoncl

A fouled or damaged TPS will also screw up the shift points if it's an automatic. For the older Renix, the dual output TPS used with the automatic transmission is cheaper than the single output version used with the manual transmission. If you don't mind an extra connector hanging there unused, you can save some money buying the automatic version.

arpunk

@lawsoncl I’m still trying to wrap my head around how a part with extra wiring costs less. Maybe they’re made in higher quantities. For testing I’ll probably get the most expensive one I can find. Not sure what MOPAR’s return policy is - I think five days and only if defective. I swapped the IAC back to the original and returned the old one. I may know a guy who can test the RPMs.

I called Chrysler, three jeep dealerships, and two shops. No one could give a definitive answer on what the RPMs should be at. Underhood sticker says “no adjustment needed” and FSM is silent on the issue.

I’m going to sand and paint the intake manifold heat shield today so I’ll see where things go Monday. If this problem never gets resolved it wouldn’t bother me too much.

For anyone interested, I am almost positive that the TPS screw size is #8-36 x 1” which appears to be nearly extinct at every hardware store I’ve called.

MJ/XJ Owner

I am just speaking from when I worked at the dealership, which was 20 years ago. I wish I could remember the exact percentage the tps showed at idle, if my memory serves correct I believe it was about 12 to 13% on our DRB scan tool. If you were reading 17% TPS the ECM was seeing partial throttle and would open the idle air motor to increase the rpms. It was a big problem on the 87-90 4.0 liter. We would see the problem if customers pressure washed their engine and got the TPS wet, they would have idle racing problems. Also earlier 87-88 models had the engine harness connection at the firewall, which caused a lot of issues with moisture intrusion and connection problems with the TPS and crank sensor. 90 model did not have that issue, just reminiscing.

arpunk

See that’s interesting what you’re saying about 12-13%.

-When I first checked the output, it was set to .62 which would fall in the 12-13% range. No issues whatsoever at idle or while driving.

-Popular suggestion is to set output voltage to 17%.

-FSM says to set output to .85 which would be 17% of 5V.

MJ/XJ Owner

If you have adjusted it to 17% then set it back to12% and see how it runs. If you have NOT adjusted it or the throttle blade which will move the TPS setting and its at 17% you may have got contamination in it or the plug. A lot of times when we had this problem we would dry everything with compressed air and the problem would go away. You could actually watch the TPS% change by just blowing air into the connection. I would also like to say the percentages I'm telling you are just off of memory an not from a manual. Another thing the factory used blue lock tight on everything and you should heat the screws to loosen it up before attempting to loosen.

arpunk

Yes I adjusted it to 17% thinking it was out of spec. FSM also says to set to 0.85V which is 17% of 5V.

However, I don’t know if someone messed with it previously. The screws didn’t appear to have any loctite on them and boy are they fragile!

Once I get the injectors back in I’ll go back to .63V and see what happens. Thanks for your input I appreciate it.

MJ/XJ Owner

You're welcome. I hope it helps.

arpunk

Oh I’m sure it won’t. Any love I give to the Jeep it returns the favor with a punch in the face.

I’m painting the heat shield right now so I expect it will pay me back by blowing out a tire.

cruiser54

.17 X input voltage. Or a little less.