Hunting idle

[Ant3R]

Hi All,
Yesterday out driving and as I pull up to a junction, the idle starts bouncing up and down.

No obvious vacuum leaks other than a pipe to a now defunct boost gauge but even when that’s covered it doesn’t make a difference.

Car still is fine starting hot or cold and drives fine etc.

Anybody got any ideas?

Jake from the forum popped over earlier and had a Quick Look, he couldn’t see anything obvious earlier.

Thanks

Ant

 

[jdmr_neil]

If it just started is almost certainly a vac leak. Cracked hose, loose fitting hose.

Other things to check are throttle cable adjusted right. If it cracks the butterflies at idle that would be a problem.
Fuel filter maybe as injectors flow low duty at idle so would be affected by a dirty filter more I guess

 

[Jake_rorx7]

We checked throttle cable, if anything it was loose, so I tightened it a little, still enough play in it to close.
Dashpot was a bit far out (as in set up to not be used much) so I adjusted that. Throttle definately closes on the stop.
Vac leak was from boost gauge, I thought aha this is it - covered it up with a finger, no change in idle. Hmm. No obvious vac leak hissing from anywhere else.
Top ground strap melted, cleaned it up but not reconnected as we need a new strap or crimp. I cleaned the battery ground behind the headlight to ensure there was at least one good ground.

Interestingly, the high cold idle on start it did (2500rpm smooth) @Ant3R said was new after this issue pronounced itself. As soon as it hit the 50c or so, bam it dropped and went back to wah-wah-wah bouncing 1200-1500rpm. We tapped the throttle when it was cold idling and it didnt drop like I thought the AWS is supposed to.

Possible thermowax issue? How can we test? I tried operating the arm on the thermowax stop but idle still bounced.
Poissble IACV issue? How can we test? Interestingly, turning on AC or headlights did not change the rpm at all as I'd expect it to, however it is bouncing above what it should be at (900?) so maybe its not a great test.

I disconnected the MAP sensor to test if it was possibly dead, it stalled right out, so definately not that...

Seems like standard vac line setup with original hoses under manifold. So might be a manifold off job ro redo the hoses, check for leaks under there? How easy are the solenoids to test? I have a 12v probe so hopefully pretty straightforward...

 

[RichLD]

Did you ever solve this issue mate? I’m having the same problem

 

[Jake_rorx7]

Did you ever solve this issue mate? I’m having the same problem

Nah we didnt, he is going to a specialist I think