Rough Running Engine First 3-4 Min

[blichjr]

Newbie here so not sure what is typical for a 911 turbo (1989) on start. When I bought it a few weeks ago seemed to run fine but on occasion a little hard to start. Ambient is 80's. Took to mechanic to replace failed reg/alternator and plugs/wires - #6 was misfiring badly - cracked extension. Working well now when warm. But on cold start runs rough, some backfire and stutter the first few minutes. Almost feels like it is going to stall. Then when beginning to warm up 3-5 min later it runs fine.

While in for repair, learned that cat converter had been removed when I bought it. Half of the EGR system removed (passenger side) and exit from muffler was wide open from the removed tube. Had mechanic plug the muffler tube and they also took belt off of the EGR blower on the drivers side so both banks were without EGR. Previously half of the engine was running on EGR, other half was not. Mechanic reset mixture and timing. Distributor is set as far clockwise as it will go. Tried to move distributor a tooth but it was too far the other way.

Any recommendations for setting an engine with the cat converter removed and EGR system disabled? Any long term problems having them removed/disabled?

Thanks!

[Bob Kontak]

Sorry for rambling - blame the stout cup of coffee I just downed. :-)

The EGR system is actually not an exhaust gas recirculation system, it is an air injection system that pumps fresh air into the exhaust to burn it some more. EGR systems go in reverse and pump exhaust into the intake when you are only cruising to dilute the fresh intake air so it cuts down on nitrogen oxide emissions. Something to do with real high temps in the combustion chambers - if the "dead" air is introduced, things cant burn as hot. 911/930's don't have EGR in them. (maybe the newer ones?)

That said, half your engine was not running on EGR. Also, the air injection system does not impact the engine, it impacts the burning of exhaust.

Regarding your issue(s) I am betting that one of the CIS components is tired.

For example there is an auxilary air regulator on your car that sneaks some air past the throttle for a couple of minutes to assist in cold running. If that is not functioning (stuck closed) , you may have symptoms like you describe.

You can pull and test this one yourself as it's easy to get to on a 930. It is on the rear bumper side of the engine and looks like the picture below.

Pull the intercooler (I think you have to to get to it) and remover the part. Look in the snoot hole and you will see a disc. That disc has a hole in it that when cold will show a partial moon shape of the hole. As the car warms that disc spins slowly and the hole goes away (all that shows is "disc") and no air is allowed to bypass.

Now that it is off and you understand the above, put it in the fridge for an hour. More hole should be seen (COLD) . Now preheat your oven to 150 degrees and bake the bad boy for 10 minutes. Pull it out and look in the snoot. The hole should have disappeared.

That is the simplest test for overall functioning. You can also close it off using 12 V but I am more interested in seeing if it is stuck in the closed position not letting air in on startup.

Actually you can use a mirror and a flashlight while it is mounted on the car to see if the disc is working. That would be THE simplest method.

Incorrect cold control pressure can cause issues as well but that will require test gauges. And of course air leaks are always a problem but they will always be present - not just for a couple of minutes.

Here is what the Aux Air Reg looks like.

[Bob Kontak]

Originally Posted by blichjr

Any long term problems having them removed/disabled?

None that I am aware of.

[Bob Kontak]

This is off topic but worthy of note given you are new to the 930.

Low mileage 89 930 sat for quite a bit and would not develop boost consistently. Wrestled with it for a long time and finally took apart the unit below the intercooler and examined the plastic lightly spring loaded valve(s) in there. They were gunked up big time and would not move properly.

Cleaned all up so they could slide with new end gaskets and car ran like a beast. I am only saying that if the car does not scare you to death giving it the beans, this is an area that may be causing some boost issues. Just hip pocket info.

[blichjr]

Thanks Bob. That is a big help. I'll have a look over the weekend. And thanks for the explanation on the EGR system. It seemed to work fine for the first week or so, and then after the mechanic did the plug/wire replacement, re-timed it and played with the mixture this stuttering problem began. Not sure if he knocked something loose or what. If it is as simple as removing the aftercooler I'll have it done quickly.

I always thought the 930 was cool as hell, and wanted one since I graduated from Engineering school. Just took me 25 years to (a) afford it and (b) convince my wife! (b) was the hard part.

Really thrilled to have stumbled onto the Pelican site. The help from you guys is awesome. Feel like part of the 911 cult group already. As I gain more expertise on this cool car I'll be able to contribute. By the way, the turbo kicks in beautifully - about 0.7-0.8 Bar. Friggin awesome.

[nut11]

This may seem overly simplistic but your Idle Control Valve may be dirty and sticking which will cause your symptoms which were exacly like mine. I took it off, soaked it in solvent, and then sprayed the inside w/ carb cleaner. No issues afterward. Good luck.

87 blk coupe
11 GTI

[blichjr]

Thanks Nut! I'll give that a try! Weekend went to heck in a hand basket and haven't pulled the aux air reg off yet so will try that first.

I do have a quick newbie question: On start the engine lets out a puff of white smoke. Clears right up and doesn't seem to smoke when driving. It also sputters for a couple sec when I turn the key off. Is that normal for a 911? Can allegedly has 30K on it.

[spuggy]

Originally Posted by blichjr

On start the engine lets out a puff of white smoke.

White smoke == Condensation. Normal on cold starts/days.

Puff of light blue/grey smoke on starting; pooled oil that leaked past an open valve overnight. Also normal if clears within a few seconds of starting.

It also sputters for a couple sec when I turn the key off. Is that normal for a 911?

930 != 911. Many similarities, but many significant differences too.

The 930 has what the import crowd would call a "turbo timer" circuit; runs the motor for a few seconds after you switch the ignition off. Believe it's to allow the turbo to spin down safely with oil delivery/pressure, also heard a theory about burning off the excess fuel in the lines from the fuel distributor.

Pretty sure this is the yellow relay (I don't have one); many of these don't work - sounds like yours does. Really don't need it, if you don't switch off the ignition with a red hot turbo still doing 100,000 RPM - couple of minutes cool down (no-boost) driving is fine.

Your cold running problems could be anything Bob already mentioned/anything you find on a regular CIS 911. If the seals on the recirculation valve are bad, it can normally be heard banging shut/open as you open/close the throttle.

930's grew extra "stuff" over the years. There could be more to worry about on the '89.

If you had half the air injection system disconnected and open, you should check a few things very carefully....

I'd be inclined to check cold control pressure first (this could well cause your poor cold running). The WUR could be out of spec; many folks opt for one modified to have separately adjustable cold/hot control pressures.

Check the idle CO2 %-ge when warm; if it's too low (lean), poor mid-range throttle response and/or lean surge will be evident.

Checking timing, control pressures, fuel delivery to the injectors, boost enrichment and AFR's under boost should be done as a matter of some urgency - certainly before you get on it hard.

These are quite critical on a CIS 930. There is no safety margin whatsoever if these aren't right. Under boost, it can go horribly wrong in single-digit seconds.

[blichjr]

Thanks Spuggy - good to know that the light smoke and sputter are fairly normal. Was a bit worried about engine wear.

Will do some research on the control pressure tonight and educate myself on that. I did have some very mild surge (noticed when on a flat road going 35 MPH or so) but had the timing and AFR adjusted and that has gone away. But the cold start thing appeared. May be coincidence or he got the AFR a little off. All the ancillary mechanical work I'm comfortable doing, but need to learn more about this engine before I'm comfortable having a go at the more advanced settings. I am really looking forward to that journey though!