Cold start tick-over problem

[triplewhite]

I'm having problems when I start my car from cold. It starts every time no problem, and I can gas it a little, but if I let the revs drop below 2000rpm, it wants to, and does stall. The only remedy to this is to keep the revs at 2000rpm for around 30 seconds. After this it runs perfectly. I plan on doing an electrical service on the car very soon, I just wonder if I should be looking for something else while I do this?

The car is an '87 Wolfsburg. Could this be a 5th injector issue?

Thanks all.

[Calimus]

Could be a 5th injector issue, but my money is on a vacc leak or mixture is slightly out of wack. Crabby cabby was like this as well and it boiled down to 3 poor injectors (spray looked good, but there was a small drip on the back of each injector which is worse then not spraying at all) and the fuel mix being way out of adjustment.

Checking for vacc leaks is pretty easy, fuel mix on straight CIS to me is a headache, but it's not hard to do by one's self. Chances are good it needs to be richened up a tad at idle to counteract the cooler air.

[triplewhite]

Ok great thanks!

[kamzcab86]

http://www.cabby-info.com/cis.htm

[triplewhite]

Cool thanks, I'm going to play with this tomorrow!

[triplewhite]

Ok.. I've done the electrical service, and checked for air leaks, and haven't found any. Do you have any advice as to what the next step should be?

I'm leaning more towards it being a fuel problem, leaky injector possibly... I know it's not good to do this from a cold start, which is why I want to fix the problem, but if I start it from cold, and get the revs up above 3k, it won't die, it will remain constant, and then after 10 or 15 seconds the revs will rise, even though my foot hasn't moved. If I start it, and don't get the revs up that high, it will consistently die, unless I floor the gas, opening the second choke, then it is recoverable from the stall, but I still need to keep the revs up until it clears... Could this "clearing" be flooding from leaky injectors?

Once this has all been done though, the car runs perfectly, no flat spots, no hesitations, which is why I think I can rule out the air leak.

Thanks...

[kamzcab86]

Test the cold-start valve (aka "5th injector"); it could very well be faulty.

[triplewhite]

Test the cold-start valve (aka "5th injector"); it could very well be faulty.

Ok thanks, how do I do this?

[kamzcab86]

If someone doesn't beat me to it, I'll let you know tomorrow... don't have Mr. Bentley with me at the moment.

As I recall, it involves removing the cold-start valve, running the fuel pumps and seeing how much fuel it dispenses. If it's not within parameters or is leaking, it's faulty.

[triplewhite]

Got ya, thanks!

[kamzcab86]

Alrighty, here's the procedure, per Bentley:
1. Make sure the engine coolant temperature is below 86°F.
2. Remove the two screws holding the cold start valve to the intake manifold. Without disconnecting the fuel line or the harness connector, remove the cold start valve from the intake manifold.
3. Disconnect the coil wire from the center tower of the distributor cap and connect it to ground, using a jumper wire.
4. Wipe dry the nozzle of the cold start valve. Point the valve into a transparent container, and have a helper actuate the starter.
5a. The valve should spray in an even, cone-shaped pattern until the thermo-time switch interrupts the circuit. An irregular spray pattern indicates a dirty or faulty cold start valve. If the valve does not spray at all, test the thermo-time switch.
5b. Wipe the nozzle dry. The nozzle should not drip for at least a minute. If it does, it is faulty and should be replaced.

[triplewhite]

That's great, thanks for this... I took the cold start valve out and the tip is black and dirty, so I cleaned it, but I've not done this test yet... Tornado sirens are sounding in Memphis at the moment, so I'll do it as soon as it's safe!

What is the best way to test the thermo-time switch?

Thanks again for you time.

[gull]

If that doesn't fix it, it's probably a mixture problem of some sort. Either the base mixture is off or the warm-up regulator is bad. The latter is easy to test with a fuel pressure gauge.

Mixture problems tend to show up more when the engine is cold because the oxygen sensor isn't operating yet, so the fuel injection system is basically working on a blind guess at the right mixture. Once the O2 sensor is hot the Lambda system will correct for an incorrect mixture, within its limits.

Another dead giveaway that you have a mixture problem is if pressing the full-throttle switch with your thumb makes the engine run better. The full-throttle switch automatically enriches the mixture, so if the engine idles better with it pressed your base mixture is probably too lean.

[triplewhite]

Thanks, my O2 sensor has been bad for a while so could that be a contributing factor? I'll run through all these tips, thanks again!!

[gull]

Thanks, my O2 sensor has been bad for a while so could that be a contributing factor? I'll run through all these tips, thanks again!!

The O2 sensor doesn't affect cold starts. Even when it's working it only takes effect when it gets hot, which takes a few minutes. I suppose if it's bad and still plugged in it could cause problems with false signals, but if you know it's bad I assume you've already unplugged the wiring harness for it.