FRporscheman

Sounds like a lot of people have this problem...

Let's all figure it out!

944Ross

Well, my 84 is the one that does it for me, and it has brand new fuel pump, new FPR, most everything in the ignition is new or verified. The O2 should not be a player on a cold engine within the first minute at least.

Is it possible the evaporative emissions system is purging during this time, and leaning the mixture?

supes6

Still there... started my car up this morning and had the usual idle divebomb - followed by the engine dying. On second starting attempt it idles low and then eventually levels out. Also stumbles on acceleration for about the first minute or 2 of driving. I'm at a loss.. and running out of ideas. Here's what I've replaced so far in the last 6 months:

-belts + waterpump
-all vacuum hoses
-plugs, plug wires, cap and rotor.
-throttle body re-seal
-fuel vapor purge valve
-dme temp sensor
-TPS
-ISV
-fuel lines
-fuel pressure regulator
-injector seals
-swapped the AFM and tried wiper arm fix inside AFM
-fuel pump check valve

My only thought is a possible leaking injector, but read that you usually get smoke on startup which I haven't noticed.

supes6

I followed this lead for a while (vapor purge system).. and replaced my thermo switch just to be sure. But I don't know enough about how the system works to be sure it's not still causing problems.

944Ross

Put a pair of pliers on the vac hose that goes to the whole mess. If your charcoal canister has lost all its charcoal, it's like a vacuum leak to atmosphere

87944turbo

Had similar starting issues when my HG was on its way out. Coolant would leak into the cylinders when shut down and would cause hard starting/misfire for a few seconds on startup. No other issues, so it was a slow leak and not a complete failure. Pull your plugs after hard starting to see if they are wet.

supes6

did you have white smoke on startup? I asked my mechanic if it could be a headgasket issue and he said there would most likely be smoke from the coolant, which I haven't seen.

87944turbo

I didn't have any of the typical tell tale signs other than the rough starting which lead me to pull the plugs and found that #4 was wet. If I had run it that way for a while, I probably would have seen coolant loss over time, but I never saw any smoke.

FRporscheman

My 84 has the issue where it really stumbles and has no power for the first 10-15 seconds of running when cold. I always thought it was a leaking injector....

How would I test for this? pull plugs first thing in the morning and swab for fuel?

black944 turbo

supes6, I have done all of the same things you have and have had my injectors rebuilt. The only thing I haven't done was the check valve. I am not loosing coolant and have checked my plugs and no signs of antifreeze. I am at a loss. I was hoping you would come and say that it fixed your problem.

My car starts rough and normally will die, restart and it runs perfectly fine with exception of being very slugish until warm. I have checked compression and leak down all comes back great, I loose less than 1/4 quart of oil each oil change. I can't figure it out.

944Ross

Some of the cars with the worse symptoms (like actually dying), I have to wonder if they aren't just worn? How many miles do you have on it? As many early cars have broken odo's, mine included, it could just be time for a rebuild...

FRporscheman

My car loses some coolant... but REALLY slowly.

How about a computer fault? Or something wrong with the O2 sensor?

teamking

I have the same problem with my 86 951 and have just always assumed it was that the O2 sensor had not yet warmed up and the fuel injection is running in open loop mode.

I suppose one could verify this by pre-heating your O2 sensor (by wiring up the 2 leads that form the heating circuit to 12v) for a minute or two prior to starting, just to see if that has any effect. (I'd volunteer to try it, but my heating circuit is shorted to ground so I snipped the wires and now have a two-lead O2 sensor rather than a four-lead).

vt951

I am having the exact same problem now, too. Just started last week. I literally just replaced the FPR a week before the stumbling start problem started, due to extremely high fuel pressure found in the rail (have a gauge there). This all leads me to believe this is more likely a fuel related problem.

So, I see lots of possible causes here:

- check valve at fuel pump
- idle valve
- O2 sensor
- head gasket leak

I was also wondering if an intake or vacuum leak or reference sensor connectors could cause this problem. I have started hearing a hissing noise under the hood in the past couple months, so I think there is an air leak somewhere. I know my ref sensor connectors are flakey because sometimes I have a no-start problem that is resolved by jerking them around.

I guess my thought for troubleshooting is to first follow 87944turbo's advice and look for a wet plug, since that's free and would have dire consequences to ignore. Then try the fuel check valve since it's fuel related and apparently cheap?

I don't know anything about the idle valve. Is that just the screw that you use to manually adjust idle, or is there some other active device? I doubt the adjustment screw is the problem because it idles fine after it gets past the stumbling problem.

944Ross

I believe the whole point of it running in open loop is that a cold engine won't run at stoichiometric ratios; maybe it's the opposite, that it is trying to run in closed loop?