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Idle issues and I have searched...

TK99XJ

NAXJA Forum User
Location
Los Angeles, CA
1999 4.0 AW4 82K...

Cold start idle is normal, after about 5 minutes it starts it's gradual climb to 1500 or 2000 and then falls off, sometimes stumbling and actual stalling in gear, I actually have to flop her in to neutral to keep her running at lights.

TPS and IAC have checked out and the voltages are within spec, I have checked all of the vacume lines and there appear to be no leaks (45 minutes looking at the lines inch by inch). I have disconnected the battery for 12 hours to reset the PCM and it has not helped and before doing so, I ran an OBDII scanner on it for codes and found none. The throttle body has been removed, IAC and throttle body were cleaned throughly with Intake cleaner.

At this point, I am not sure where to go next. she runs fine at speed so I do not think fuel pressure is an issue.

Any suggestions would be great!
 
I am about 95% sure that there is a vaccum leak at the intake manifold. Check the torque on the bolts, they probably rattled themselves loose after all of the years. Check tp top ones first, if they are loose then attack the lower ones.

Tell us how it goes.
K
 
Ok, checked the bolts on the intake and all were torqued to spec; WD40'd around the intake gasket to see if that would level out the idle, of course it did nothing. WD40'd the base of all six injectors to see if there might be a vaccume leak there, did nothing.

Disconected the TPS to see what that would do and bingo, the idle leveled out immediately. What is weird is that the voltages out of the TPS are correct, so I bought a new one and tried it. SAME THING happened, idle all over the place; she even died twice in gear.

I am soooo confused. Still no PCM codes, I dissconected the battery again to see if that would reset anything with the new TPS, I'll let you know.

HELP ME?!?!?!
 
Getting a lot of unbruned or fuel rich smell at the exhaust and the misfire seems to be getting worse.

No carbon tracking that I can see on the inside of the distributor cap; I went ahead and ordered a new one anyway with a rotor as well.

I am going to run the scan tool on it again tonight, see if there is ANYTHING that might have coded in the last couple of days.

Any other ideas out there?
 
I did not realize that we were talking about a 99, I would not have suggested the intake manifold. I do not know how I missed that.

It does not sound like a regular vac leak. I regular vacuum leak the idle would be high the second you started and not go away.

I would suggest pulling the throttle body off and cleaning it if you have not already done so. I would take both the IAC and TPS off and pull the TB off. Dunk the whole thing in gas, kerosen, carb cleaner, whatever. Make sure the tip of the IAC is clean.

I have an 89 so it is a bit different.

K
 
No problem on the year Katarn, I do the same thing here a lot.

Already did the TB, took it off, cleaned everything with intake cleaner, the IAC was removed and the seat where the piston is positioned was cleaned with Q-tips along with the piston it's self with no luck.

Once I run the codes again, if I find anything there I'll post it ASAP. I promise to keep a log on what transpires.

Any other suggestions are always helpful!
 
Is your CEL light on? Also, check MAP sensor vacuum line, they can deteriorate or crack, check the whole thing. Dont get WD40 into your intake as it can kill your o2 sensor.
 
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