1.8 ecu and tcu I can't.get a consistent reading. It flashes 7 then goes infinite....

 

Yeah, the TCU ground acts weird. Don't worry about that. The one to the ECU is 1.8? If so, with your meter hooked up wiggle the harness near the injectors and then near the MAP. What happens at the ohmmeter?

 

No change.

 

That's good. You know what the C101 connector is right? The connector on the firewall above the brake booster. Unbolt the two halves, scrape the tar looking crap out with a small screwdriver, spray it out with electronics cleaner til pretty clean, especially the pins and receptacles, add dielectric grease and bolt it back together. Now see where your resistance is. You're only a bit high but it's worth getting rid of. Besides, cleaning the C101 is ALWAYS a good idea if it's never been done at least once in the lifetime of a Renix Jeep.

There's another more radical approach to eliminating the resistance in that circuit if you're ever interested but let's see where the C101 cleaning takes us..

 

Ya I forgot about that one when I cleaned everything. As I understand it this is grounded through the ecu not static correct? As a buffer against power surges? Oh ya.... my main harness is down and to the right of the booster BTW... guess that's why I never bothered lol

 

Sensors ground through the ECU. Also be sure the ground connectors at the engine dipstick tube stud are cleaned and refreshed.
You can ground the sensors separately if you like but there's a better way to do it. If you need to, I can provide the info.You don't have a C101 on a 90. Sorry, they're only on 87 and 88s. You'll need to crack open the harness and do some soldering. Very easy..

 

dont know if this wil help or not, but i was having the same problem with my 99 xj. my idle problem was caused by the pre-cat O2 sensor, i replaced it about 3 weeks ago and havent had a rough idle or loss of power since, and this was after i tried the iac and the cps sensors as well. i was told by my mechanic that my O2 sensor was working which is why it would not cause a check engine light, but that it was lazy when transfering from the delay start and running position. i was also informed to get the O2 sensor from a factory direct jeep dealer due to the fact that the aftermarket sensors are less responsive than the originals. either way my jeep runs and idles great now, hope this will help. good luck

 

i know this is an old subject but id thought id update

took it to a shop and hooked it up to a scan tool...the O2 sensor is not reading corectly and you can see it goiing in and out of closed/open loop, you also see the short term fuel trim going from 128 to zero and back....so the tech suggested i replace the O2 and go from there.

im going to replace it this week and ill let you know if it fixes it

wish me luck

 

finally got around to working on my jeep...so to update i replaced the O2 sensor and it fixed my idle issue....now that it runs right going start working on other things....but first i now need to replace my battery it wont hold a charge anymore

 

Glad to hear it and thanks for the update.