Cold start/idle issue -
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post #1 of 1 Old 03-13-2012, 06:01 PM Thread Starter
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1999 TJ Wrangler 
Join Date: Nov 2006
Location: Marcy, NY
Posts: 356
Wj Cold start/idle issue

Hey guys, I tried to do my own research on this one but I'd appreciate some fresh input. For reference, my WJ has 231,000 miles on it.

I am having an issue with cold starts (not necessarily cold temperatures per se, but say after the Jeep's been sitting 8 hours or more).

When making a cold start, the engine will not start unless I have my foot down on the accelerator ever so gently. If I use my foot to maintain around 1000 RPM's, and hold it there for about 45-60 seconds, I can then release the gas pedal and the Jeep will idle at about 600 RPM's on it's own (although it's a rough, rich smelling idle).

Once the Jeep is driven for 5-8 minutes or up to normal operating temperature, it will then idle perfectly. In gear and in park, once it warms up, it idles just as it should, smoothly and at the correct idle speed.

The problem existed for a few weeks with no CEL, then it finally tripped a code P0135 (1/1 upstream O2 sensor).

The following actions were taken:

-Cleaned battery connections and inspected grounds. All appear OK.
-Sprayed (liberally) throttle body cleaner into IAC valve slot in throttle body with Jeep running. Also applied it to throttle body itself and removed quite a bit of gummy crap from TB.
-Checked IAC wiring and connections (ok)
-Checked 1/1 O2 sensor fuse (#16) - It's intact. I pulled it and cleaned the contacts anyway.
-Changed factory upstream O2 sensor (which I found on only finger tight) with Denso 234-5488 replacement. I heard that Denso's were ok to use...
-Cleaned battery terminals AGAIN, removed positive cable while I was changing the sensor (took about 45 minutes). Applied brake with key on while POS cable was off (attempt to reset PCM).

After all this, the Jeep WILL now cold start without my foot on the gas, but it idles poorly (about 600 RPM cold) and sounds like it's ready to stall. After about 4 minutes the idle smooths out and comes up to about 900 RPM. The Jeep drives fine - has all the power it should and gets around 13.5 MPG.

What should I do? TPS, IAC? New battery? I heard about the wire loom that runs along the back of the engine but mine appears intact and not rubbing on anything, although I did NOT split it open and check each wire...yet.

Thanks for any input.

1999 TJ 2.5L AX5 NP231 D35/30 4.11's
*Disclaimer - I've probably had a few beers
nhcd538 is offline  

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