Follow-Up to Carrera Stalling in Hot Weather

[RandalJ]

A few weeks ago I started a thread on a problem I had with stalling in the hot afternoons here in Phoenix. I just wanted to follow this up with what I have found.

Just to reaquaint you with the problem, my 86 Carrera with 77k miles would intermittantly stall, usually during warm-up, in higher ambient temperatures. It would start and idle just fine at first start-up, and would also start and idle just fine after every time it stalled. It would usually stall after driving a short distance, when I would put the clutch in for a stop - at a stop sign or a red light. Or if you blipped the throttle when sitting at idle. The tach would dive to zero, sometimes recovering to normal idle, sometimes not. Having the A/C on was an additional load that would aggrevate the situation. Otherwise, driveability and acceleration are strong.

I had had a major service done by a very reputable shop (Stuttgart SW) last September when I bought the car, so I had pretty much ruled out ignition related issues. Besides, I did recall having this stalling a few times during the few weeks I had the car, after the service, but before it got cooler in the fall. I had sort of forgotten that until the stalling began happening again in the summer.

I did pull and disassemble the idle air control valve, and posted a photo here, showing a large pit on one of the armature contacts. I replaced the valve, and thought I saw improvement, but we had also had cooler weather here, and that gave misleading results. The stalling was back when it got hot again.

I then tried to lean the mixture on Steve Wong's advice (I have an Autothority MAF and chip, so it was easy to do by tracking the resistance reading). That helped considerably. I still get the stalling once in a while, but not nearly as often as before. So, while the problem is not 100% solved - the tach still does the dive thing in hot weather, but recovers 98% of the time - it is much better than it was. I have experimented with different idle mix settings, and cannot seems to get further improvement.

I have a valve job on the horizon, for a worn valve guide, so I am hoping whatever remaining issue(s) I have will be sorted out out then. In the mean time, cooler weather should take care of the problem once we enter the fall months.

So, my conclusion so far is that the system does not like a rich idle when ambient temps are high - like 90 or above. It has a real tough time when temps are above 110 unless you lean out the idle mix.