IAC behaviour / still having bad start (4.0 renix)

[JE39]

Hi!

 

Just out of curiosity; the IAC seems to be rather new. However it was not me who installed it, but the PO. I had a starting issue, and sometimes after startup idle would "stick" at 1000 or 2000RPM. Sometimes idle is very low and the engine stalls. And sometimes after cranking the revs go up for a very brief moment and drop to idle speed (within less than a second). I think this is how it's supposed to work. I pulled the IAC - looks just as clean inside than outside. I oiled it anyway, which seems to have improved things a LOT. I have no more high idle.

 

After I replaced & adjusted the TPS, I also have a lot better starting. But - the engine still struggles most times to maintain idle the first few seconds after cranking. And when cold, I have a little flat-spot when pushing the accelerator down FAST.

 

Now what I wonder about is - I was able to push the IAC in - but was not able to pull it out by hand... Is this normal, or is the IAC faulty?? I suspect the IAC is my issue. But before I spend any money,, I'd like to hear a few opinions. 

 

Thanks for your thoughts! :)

[jeepdude89]

I had the same issue on my 88 4.0 MJ and I was able to fix it by cleaning up the contacts for the idle relay which is located on the passenger side behind the battery. It has never happened again after that. The relay is called the power latch relay.

[jeepdude89]

Here's a pic showing where it's located.

[cruiser54]

Here is ONE thing you should do on your Renix and it is an expansion on what was stated above.

 

http://cruiser54.com/?p=35

 

Also, who's procedure did you use for adjusting the TPS?

 

See Tip 5 below.

 

http://cruiser54.com/?p=44

 

 

[JE39]

@jeepdude89 Thanks a bunch! I'll try that. 

 

@cruiser54 I've allready cleaned the C101 and all grounds I found, following your advice :) Guess I just have to do more cleaning. I adjusted the TPS following the factory injection manual, which states to just "adjust as close as possible to 0.8V". After I've done this, the engine runs much smoother. I probed the connector with some pieces of wire and high quality tester cable thingys (don't know the proper term).

 

However, I did not yet actually  measure resistance - I'll do that as soon as possible! Thanks!

[cruiser54]

Factory procedure is wrong. 

 

Do Tip 5--http://cruiser54.com/?p=44

 

When that's all good, test/adjust your TPS like this--http://cruiser54.com/?p=54

[JE39]

Hmm. Ok, going by a percentage of the actual input voltage (instead of a fixed output value) does indeed make sense. I'm going to re-adjust it. Thanks! :) 

[cruiser54]

That's PART of it.

 

Use the flat connector and it's percentages.