high idle at start up and shifting problems

88 4.0 AW4 242 30/35


i'm thinking from searching on here that my TPS may be on its way out. The problem is that when my jeep is started it will sometimes rev to nearly 3k RPM and stick there. IT seems the higher it revs on startup the more stubborn it is to calm itself back down. while its revved up i'll try to tap the gas on occasion to get it to calm down and it just stays to where ever i reved it up to. as for the shifting problem i'm having, its taking a longer time to shift to the next gear during normal daily driving activities. sometimes it wont catch the next gear until i let off the gas then it will upshift. the trans oil looks great and is full.


if it is the TPS does someone have a writeup with pictures of how to adjust it. I've read about it alot but i can't seem to get the concept of it. i think the problem lies in my inexperience with a multi meter.

tia

Another TPS thread? How many times does it take to become "Frequently asked" and end up in the FAQ section? Sorry for sounding like a whiner, but I know I'm not the only one that feels this way. As for the question at hand: use the advanced search feature, and try and find a link for pirate 4x4, they have a link to some helpful manuals. I don't think that I am violating the FSM link rule but if I am, I'm sorry.

thats just the problem to much info to scroll through. Plus i wasn't completely sure if it was the TPS. I'll search for the link to pirate4x4 and see what i can come across. I've been on here long enough to know that many questions get asked time and time again, however this is a new problem for me and i didn't come up with anything concrete from searching. thanks for the help and the direction though.

I've been have this same problem for a week now. Everyday at least once. I happened acouple weeks ago real quick but I figurered it was a qurik but now it keeps happening. I'm going to go crazy.! BTW. My TPS is new since jun 06 and approx 10k miles so that leads me to think otherwise off the top of my head but who knows? OH, and yes shifting issues included also.

The usual suspects for automatic, AW4 tranny shifting problems is the TPS, the wiring to the TPS, and any engine, firewall and battery GROUNDS that can affect the TPS to TCU (Transmission Control unit) signals. A bad, or even worse a variable, loose dirty ground acts like a foot on the gas peddle to the ECU and TCU!!!!

The usual suspects for high idle problems is the TPS (ECU side, the TPS is a dual sensor, two sides on the 87-90 Renix models), the wiring to the TPS, any and all sensor, engine, firewall and battery GROUNDS and the IAC (Idle Air Controller) and the B+ latch relay.

When the engine shuts down the ECU stays on and powers the B+ latch relay long enough to reset the IAC for the next restart. If that fails to happen it can cause start up idle problems. If the IAC sticks it can stick at a high idle position. They get dirty and sticky from carbon buildup, and need cleaning and oiling about once a year,

The IAC and TPS are mounted on the throttle body.

www.lunghd.com and www.Pirate4x4.com and www.MadXJ.com all have some good pictures and data, if you need the Renix Fuel Injection manual PM me, it is also available in 5-90's RenixPower Yahoo group's files section (just sign up to reach the files download area. If you search for "Ecomike RenX Files" under avanced search in the OEM tech section there is a great thread there on too on these problems, including test data never posted or published anywhere else.

Ground problems are at the engine block near the oil dip stick, several sensor grounds are there, so is the only battery to engine ground. Only engine to car frame and only car frame ground is at the drivers side rear on the engine head rear, near the firewall and the firewall itself. They should all be removed and all contact surfaces cleaned to bright metal on both sides and reconnected. Also clean and check the battery clamps and wires.

Renix is very sensitive to a few extra ohms of ground resistance!!!

Once you have done all that you need to follow the 89-90 FSM Renix Fuel Injection instructions for calibrating the TPS on the TCU side!!!!! It is the latest and best way to calibrate the dual TPS on AW4 tranny equiped XJ's. The older FSM proceudre is obsolete, but is a good final check of the 90 calibration method. The 90 calibration uses the TCU side for calibration.

Also need to check that the TPS is 5 volts from the ECU and TCU at the TPS!!!!!! If not that causes problems too, like power problems and shifting problems.

TPS's do wear out, they also hate water!!!!! IAC's get dirty and stick, wiring harness connectors get old and loose, and so do grounds. And manifolds and vacuum lines get loose and leack vacuum.

A vacuum leak, vacuum hose or intake manifold leak, or CCV ) Crank Case Ventilation) line leak can cause a high idle too!

I had a similar situation with my 87 MJ. I went to clean the IAC and reset the TPS and they were the original ones! Wow.

Anyway, after I cleaned the IAC and throttle body with some carb cleaner, the idle issue went away. You might try that first as its easy and free (except for the carb cleaner, but I had a can already).

well guys thanks for the replies but i think i've solved the problem. i've had a hissing that i thought might be a vacuum leak for sometime now but i couldn't track it down so i replaced all vacuum lines on the top of the engine. the hissing never went away so i figured it might just be my imagination. i decided to take some water and pour it around the intake manifold to see if i could hear the leak go away. It turned out to be an injector o-ring that was leaking. i replaced the o-rings and the high idle and shifting issues seem to have gone away.


thanks for the input fellas