lightemup67

Hello All,

I'm hoping to get some help with an idle issue I'm having. The motor started surging one day, running up to about 3k RPM and back down over and over. Hitting the gas will kill it, and it always starts right back up. Also, when it doesn't surge, it idles around 850 RPM, but periodically stumbles down to just about dying, and then recovers. It has died at a few stoplights, but always started right back up. Also, once its hot, it runs like a champ, this is only a cold start issue. Engine and chip are stock.

I've done a lot of research on this issue, but haven't had any luck on what I've tried:
1) Disassembled and cleaned AFM
2) When this didn't help, I "remapped" the arm in the AFM on a new track on the black strip
3) new O2 sensor
4) New 2 wire Head temp sensor
5) Cleaned and bench tested the ICV (all good opening and closing)

All of these things seemed to help a tiny bit, where it doesn't happen as often, but still happens. I'm starting to think I should look into replacing fuel injectors or looking at the fuel regulator? But I'm kind of out of ideas besides that.

If anyone could lend some thoughts, I would really appreciate it.

Thank you!

Brian

vetter59

souunds like a intake leak somewhere, vacuum hose off or gasket missing/broken. Have you tried using spray bottle with water with engine idling, spary areas one at a time and look for idle to drop - indicating a possible leaking area.

lightemup67

Thanks for the response! I did try the carb cleaner around various hoses, but didn't get any throttle response. Since it only happens when the engine is cold, I didn't think much about a vacuum leak, as I figured this would occur at all times. Worth another shot thought. Thanks!

Spyerx

Smoke test that bad boy.
Sounds like a vacuum leak

r911

how does the Mootronic system handle cold running?

you need to figure out what affects cold running vs. fully warmed up situations -- on many Bosch systems the O2 sensor will not be used by the ECU until warmed up, so where is that temperature sensor and how do you test it?

does it have a cold-start injector?

does it retard the ignition while cold?

you'l have to figure out the control system at a black-box theory of operation level, or find a checklist in a manual (Bentley??) and follow it by rote

lightemup67

Thanks for the responses! I'm going to check vacuum hoses first through smoke/ more carb cleaner. I'll post back with my findings.

09mageec

I would be careful with carb cleaner if you don't have a Pop Off Flap installed inside the airbox...

lightemup67

Update on my situation:

After looking more into vaccum leaks, I found one hose off of the back of the air box that had popped off. I think it runs to the oil tank? I was hopeful that was it, but it didn't run much better on the test drive. Going to keep looking for vacuum leaks.

theiceman

Swap the afm with a known good one.

lightemup67

That would mean finding someone with a 3.2 in my area and convincing them to let me swap the AFMs real fast? Never got how people do that without ordering a new one.

theiceman

I think you might find local rennlisters and Pelicans quite helpful.

r911

I'd check every possible junction and mating surface for air leaks first.

der Mond

Try going over every listed ground connection in the shop manual, hard copy or online. I replaced the intake manifold risers and gaskets on my '87 3.2 and had CO reset and had issues until I found that I had not tightened the connection to ground sufficiently on the intake manifold.

r911

good idea

here is a 964 diagram as there may not be one for your car & a pic of one by the fuel filler (take out some gauges) on my '73

lightemup67

Hey fellas,

Thought I'd update you on the progress.

I continued checking for vacuum leaks with carb cleaner and had no luck. I moved onto grounds and everything I've checked is clean and tight. Although I've only checked about half so far.

Last night I decided to increase the idle, and I believe the previous owner had it set with the vacuum leak present. It was low (650 to 750). I increased it to 900ish by jumping g the b and c ports on the diagnostic port, and adjusting the idle hex screw on the throttle body.

I took it for a drive, and the idle bounced around slightly at stop lights. Went home and lowered the idle a little, and it seemed to cure it. It was late, so I didn't have time to test it on a cold start. I'll do that tonight.

one thing I noticed while testing things, we're these two wires with female connectors on the drivers side of the engine bay, nother connected to anything. Anyone know wherected they are supposed to go?

Just seemed odd to me.

I'll let you guys know how the cold driving goes tonight. This is the true test.