I installed the new O2 sensor last Sunday. While I was under the XJ I saw two more gotchas: exhaust not tight because missing one of the manifold-to-downpipe nuts; CPS harness damaged by hot exhaust manifold.

Had to wait until this weekend to fix the new gotchas: replaced the missing downpipe nut and swapped the old-but-good Mopar CPS back in (and routed the harness to avoid the exhaust manifold).

Results: new O2 seems to have fixed the hesitation at light acceleration during the first few minutes after a cold start; tighter exhaust is more quiet and combined with the new O2 the XJ is running less rich now.

Today's test drive went really well -- no stumbling or hesitation at any level of acceleration, with cold or warm engine. I'll report back after more road testing.

 

good news!!

 

Well "slouthed"! Much thanks for getting back. (Worthless dirt-bags just leave after they hear what they needed) Is the idle even now?

 

Thx for the pic; I did use that harness path (this time).

Took another test drive, more extensive; good results continue in that there was no hesitation/stumbling at acceleration. I'll check it again in the morning.

 

DF, I'm with you -- it definitely hurts the thread value when the OP fails to post some kind of results/resolution.

The XJ's idle is not perfect. A wee bit of a miss/stumble somewhere in the background. Not terrible but not truly smooth; more attention needed, for sure. At startup it settles into 750 pretty quickly now, an improvement 'cause it's not hunting/cycling. But after a test drive, the idle is below 750, at 550-600rpm. Sounds like it's loafing, taking a break at that point. It revs easily but settles back to 550-600rpm.

Today I checked the exhaust after the test drive -- was looking for how rich -- and thought the little puffs coming out of the tailpipe reminded me of a Harley, with some puffs more puffy than others if you know what I mean. Not a nice even/smooth idle sequence. (At least the exhaust was more lean smelling than before; today I had to think about whether it was a touch rich; not long ago there was no doubt, it was rich.)

 

Here on post 66.... Crusier is the man....The IAC can be trouble...cleaned OK, but also if the IAC motor had ever been powered up with it out, that's a problem. It controls the airflow past the throttle plate, (like the idle speed screw of old). If the idle is low the ECU should be telling it to reverse the motor and pull that plug back farther. I'm making this up now, powered up out it might just run it out to the end of it's threads, so it can't pull it back far enough any more. Now my personal stuff... I had intermittent high idle. Cleaned it a few times checking the O ring. In the end it seemed it was the wiring connector. The sort of "female", facing up (with the "male" plugs)....that is pretty hard to clean, and the way it faces up, it can get stuff in there. At some point spraying in there with different cleaners and working the plug in and out, my intermittent high idle went away. So there is that.

I myself won't ever under estimate what the TPS is up to/ can do. Have that in specs with it's ground good before messing much with anything else.

 

Thanks for the ideas. The IAC appears to be OK but then again how would you know if it was not 100% unless you have an IAC exerciser tool? I don't think the IAC has been powered-up when it was out of the TB. And I definitely agree with your advice to get the TPS dialed-in first, output adjustment and ground.

The IAC was cleaned about a month ago; wasn't dirty. I will recheck the IAC connector for dirt/debris and spray it again with contact cleaner (Caig D5). The TPS is new and recently adjusted. The sensor grounds are pretty good, less than 1-Ohm resistance, much improved since performing Cruiser's ground refresh steps.

I have not cleaned the throttle body but I did just buy a new TB gasket so that I have it on hand if needed.

 

The line from the intake to the rear of your valve cover has the CCV orifice at the end. That's a 2.4 mm "calibrated" vacuum leak, there to guarantee airflow through the crankcase. Vacuum leaks make idle go up, and that is one, sort of. I would think the IAC would adjust the idle correctly one way or the other, but you might make sure that's line/orifice is not plugged up, causing the low idle.

 

DF, I checked the CCV vac line -- it's clear.

Test drives yesterday and today were both very positive: no hesitation/stumbling across the RPM range; engine running well, not working hard unless requested via throttle; then it answers the bell right away; definitely driveable and no longer a safety concern about wife using it as a DD for runarounds.

[I'm going to put this thread out of its misery and start a fresh one for the low idle issue.]

For the XJ's hesitation/stumbling issues, the main parts fixes were the new vacuum harnesses and the new O2 sensor. These had the greatest impact on eliminating the stumbling/hesitation problem. [SuperRA had the same advice/experience many posts ago in this thread.]

Ground/connector refreshes had to be beneficial too for the entire sensor/ECU system. And the new fuel pressure regulator boosted the fuel pressure up from 26/34 (-5/-5psi) to 29/36 (-2/-3psi). All steps contributed to a smoother running engine.

Many thanks to all for helping. I can now move on to other issues -- lots to be done...

 

Clean the throttle body. And, thanks for posting back.