Low, Stumbling Idle. 3FE

[62LostInMn]

I'm looking for feedback and some possible next steps. I've owned this cruiser since 2009 and it really always has had this issue, but it' been worse of late. It doesn't stall when coming to idle and it runs fine otherwise. Cold start is fine and it has high idle that comes down in two steps to about 600-650 as it warms up. The low idle comes in when it is really warm and coming to a stop. It's a pretty pronounced stumble and rpm drops down to about 500.

What I've checked so far:
Pulled the plugs (they're about a year old, along with cap and rotor) see pic below. L to R is cyl's 6 -1. They look a little funny to me, but not sure how.
Compression check: All 6 range from 138 to 145
On-vehicle TPS check: All within spec except the .043" shim gives 160 k-Ohm instead of infinity
On-vehicle AFM check: All within spec
Checked timing: Looks very close from the funky viewing angle I could get to, and comes up to ~12 when pulling the test jumper
Fuel pressure on the cold start injector line is in the low-30's at idle.

Vacuum at warmed up idle is about 17in Hg. I can pull a small vac hose and the idle comes up a bit as I'd expect. Pulling the dip stick or oil fill cap cause a change.

I adjusted the valves about a year ago and replaced the pcv, grommet and hose.

I've sprayed carb cleaner everywhere I can get to and do not hear any changes.

I have not done much with the EGR, other than test that it opens and kills the engine when applying vacuum to it directly. Is it possible to be stuck open slightly?

Anyway - thoughts on where to go next? I'm running out of options and would love to get this one put to bed.

 

[LAMBCRUSHER]

yes, egr can get stuck from closing all the way, but not very common. I noticed your TPS isn't giving you infinity at .043...you should remove the TB and TPS and clean the TB with TB cleaner NOT carb cleaner...seems like there may be some gunk keeping the plate from sitting where it should at .043", thus giving 160 ohms vs OL. that is going to make funny things happen. aside from that contributing to your issue, have you changed the fuel filter recently? are your cats old and clooged? have you checked into the fuel pressure system? regulator(which gets fed a vacuum line to help control flo- if the vacuum isn't hooked up or the VSV isn't working right, you could have an odd Fuel Pressure signature at that warm idle) fuel pulsation damper? if your coolant is low, then the coolant sensor could be sending funky info to the ECU...just a few things...I'd start with that TPS issue...

 

[62LostInMn]

Thanks LC.

The TPS reading with the .043 shim was actually 160,000 ohm, so it's pretty high, but not quite OL. No cats on the truck, the O2 sensors have about 30k miles on them. FPR is 2 years old and the fuel pressure looks OK. Forgot to mention that I checked the movement of the ICS by peeking through the hose connection - it appears to be moving normally, or moving anyway.

I havent checked the two air gaps in the distributor yet. Has anyone seen those out and causing problems?

Probably should just bite the bullet and take the intake apart and clean everything, send the injectors out. It would be nice to ID something for sure... We'll keep after it.

 

[bakerbrian]

I have the exact same issue on my 62. I have been trying to track this down for about a year now. Any ideas or progress would be great. Thanks!

 

[Gurr]

Anything happen with this? I'm actually getting the same sort of issue on the 2F...could be unrelated. I'm going to keep my search up.

 

[LAMBCRUSHER]

@Gurr check your warmed idle vacuum. it should be at least 16.5"; higher at closer to sea level... another thing to check is the VCV for the dizzy vent. I had one go bad and leak internally- could not find it without removing and capping all the lines...I found that removing and capping the lines to that VCV brought my idle vac up to near 20 fro 15, then tested the valve and found it to be shot. also, check the fuel filter. HTH

 

[brownbear]

I had this with my old 80, with the 3fe. I put two BB pellets in the vacuum lines coming out of the top of the manifold to shut off vacuum to the egr. Improved this 100%. Ran so smooth after. You can clamp, block or do whatever to the lines, except un hook them.Give it a try. The EGR is a piece of crap on these.

 

[Randy88FJ62]

cracks in the large intake hose going from your air cleaner to the intake manifold would cause stumbling at idle. Same with vacuum hoses.