cold start hunting/surging 3.2

[dickster]

i have a 1986 3.2

on every cold start the engine initially hunts up and down between 800 and 1200 rpm about 6 times when it settles to smooth idle. it is ok for the rest of the time after.

any ideas?

i have searched the archives and seems that it could be a number of things. i have owned the car since april and its only been like it for a couple of months.

just seems odd that it otherwise runs great.


richard

[don911]

My guess is oxy sensor. My car did that once in a while until I changed the oxy sensor. It's an easy replacement, so that's what I would try first.

[rob justice]

Snap - mine does exactly the same. The only time it dosen't hunt is after the battery has been fully charged. I don't have any charging problems but if left for a while the alarm tends to use a lot of juice. I just left the hunting as charactor!!!!!!!!

[Milu]

I think that hunting up and down is intentionally built-in on a coldstart. Stops it dying etc when you move off.

[dickster]

rob - i had to laugh at that!
i'll put it down to european charactor then


don911 - mine has done 90k and i have no idea if the sensor has been replaced so i guess it would be a good idea anyhow..

nothing to worry about



thanks guys

richard

[stlrj]

My 86 had been doing the same for years, assumed it was normal. But after pulling my intake manifold and resealing all the intake gaskets with GMS sealer it no longer hunts on startup.

A side benefit was a much smoother idle and much improved bottom end throttle response.

I have my doubts concerning your 02 sensor as the source of your problem since it will not have any influence until it has warmed up which could take a couple of minutes and by then it has stopped hunting. Besides,if you disconnected it, it probably would not make a difference.

Cheers,

Joe Garcia
Redwood PCA since 1976

[dickster]

joe - no, no, no! now i'll have to investigate! thanks a bunch! good point about the co sensor - i forgot that they need to warm up.

i'll see what i can find............



richard

[Decolliber]

My 88 Carrera did the same thing after installing new injectors. Consider:
1. Turning down the idle (turn clockwise screw facing you on the throttle body) after jumpering test port (see Haynes). This has solved the problem for me, though it still hunts 2-3 times before settling down on a cold morning.
1. Idle mixture adjustment (allen screw under left side of air flow sensor). See recent postings on how to do this.
2. Screw that holds the throttle drag arm off the idle switch; this screw (to lower left of throttle body) keeps the throttle slightly open; turning it anticlockwise will lower idle too, though this screw should really only be used to set the clearance between the drag arm and the idle switch housing (see Bentley 240 -??).
3. Hunting may also be caused by DME trying to manage a small vacuum leak (eg, at intake manifold, as already mentioned). Check your hoses for vacuum leaks too; I found several.
4. Several of my intake manifold bolts were well below correct torque (18 ft lbs).