Carrera 3.0 - CIS Surging

[OZCarrera3]

Have been experiencing surging at constant throttle openings (say cruising at 60km/h) and poor starting (missing & lumpy idle till warm). Had my local specialist tune the car yesterday and the thing still has the same symptoms. Spoke to the shop today and they told me that the surging is inherent to the Carrera 3.0 and that in all likelihood there is not a lot that can be done to correct the problem (also that poor idle is most likely due to worn injectors – would accept this). The shop has agreed to keep the car for a few days to fully check the cold starting issue and to review the surging problem.

I have reviewed a number of posts on this subject (CIS Surging) and not found anything that relates specifically to the C3 and found that other 911's with this problem have generally found the O2 sensor and lean fuel mixtures as the cause. I have only owned the car 4 months and it ran fine at first, it only started with the surging symptoms soon after the fitment of a new fuel accumulator.

My questions are:
1) Has anyone else found that this problem is inherent to the C3?
2) Could the new accumulator be faulty and cause the problem?

[amk]

Mine surges a bit at idle when cold. Usually lasts the first few minutes. The idle is fine when warmed up.

I found that even when warm the car would quite often stall when I came to a halt. I could replicate this by blipping the throttle at rest to about 3000 rpm, the revs would typically drop too far and the car would stall. I know I've got pressure leaks through the top of the injectors (need new sleeves and O rings). Until I get round to replacing the injectors I've increased the idle to about 1000 rpm (was previously set at about 900 rpm) and the stalling problem has gone away. I've also noticed that with a 1000 rpm idle the initial surging when cold is much less pronounced.

Regards,
Andrew.

[amk]

Upps, forgot to mention I've had no problems with surging at constant throttle openings, warm or cold.

[Argeo]

Try adjusting through the mixture control unit. Your car sounds like it is running rich. Just make sure the car is warmed up to operating temp, you turn off between adj (since your car is surging) and turn a 1/8 of a turn at a time. Sounds like you need to go CCW to lean a bit. I idle will probably go up a bit, but when surging is gone then adjust through the throttle body to bring idle back to reasonable level.

Sounds like if that does not work that it might be your cold start valve gone bad. Stuck open. If this is the case, the car will probably start fine for the first 15 or 20 seconds and then gradually start to go downhill from there. Anyone out there have this happen to shed some light on the subject?

Good luck.

[beamonk]

I have a 3.0 Ruro motor, it surges some on warm up, but runs fine thereafter. My mechanic said this is pretty common for euro motors, we could do alot of adjusting, which I have done, but it works good like it is, plugs are beautiful and I figure leave well enough alone.

[AZ1977911]

I've got a 1977 Carrera 3. Motor modified with 3.2 liter Big Bore kit. CIS is still stock. I have the same problem. It has been diagnosed with WUR issues. I will be replacing that in the not to distant future. Till then I user the hand throttle till warm.

Good Luck

[echrisconnor]

no surging. But I do have high idle at startup and then do sometimes stall at lights.

CIS requires someone who knows enough to run through the entire system and the symptoms of various faults. As Noah said, find someone who knows this stuff inside and out. Alternately, get a CIS fuel pressure gauge and a Gunnison exhaust gas tester and start troubleshooting.

I wish there were a good CIS 1, 2, 3 article for pre-lambda cars that showed the first thing to start with and what to look at next. Some of that is probably obvious, start with vacuum leaks, look at voltage and resistance to the AAR and WUR, check your mixture, check control pressure. Go through the CIS troubleshooting matrix...

http://www.pelicanparts.com/911/technical_specs/911_cis_troubleshoot.htm

From there I'm lost. Good luck.

[OZCarrera3]

Thanks for the feedback everyone.

Looks like the starting problem is a common occurrence to a degree and I'll look at replacing the injectors. Andrew (AMK), I had the stalling on return to idle problem and that was what prompted replacement of the accumulator, which cured the stalling issue.

As for the surging, you've all confirmed my doubts and it definitely does not appear to be an 'inherent' problem with the C3. The shop I take my car to is broadly accepted as being an extremely reputable and capable workshop by a lot of P-Car drivers here in Brisbane. I'll see what happens when I take the car back next week and ask them to specifically check the mixture and cold start valve. If the problem persists, I'll look for an FI specialist to address the problem.

Thanks again for your help.

[amk]

Thanks for the info Sheldon. I'll add that to my list of things to do.

[echrisconnor]

From past searches I believe that the stalling thing is supposed to be the deceleration valve. I can't validate this though.

[Superman]

I'm not taking the time to read all the above posts, so forgive me but....

Surging idle is one thing (classic, common situation...nothing to worry about...probably cavitation in that HUGE air box), but constant-idle surging is nearly always (in my limited experience) evidence of a lean running condition. A vacuum leak can cause this, but factory spec for these CIS engines is just simply too lean. WAY too lean in some cases. My mixture, right now, is set at about five times the factory spec, in terms of CO emissions.

[HarryD]

This thread should have some good links to help you out.

[OZCarrera3]

Rummy,

Your suggestion to check the injectors sounds good and dare I say...easy. Could you please give me a step by step instructions just to make sure. I assume you simply disconnect extract each injector and point each into a sepearte jar to catch the fuel (i.e. 6 jars)? What is the sensor plate and where can it be found (in the throttle body)? I assume this activates the injector?

Thanks for you help.

[Argeo]

Sorry, I thought you meant the idle was jumping. Sorry, I do not think it is the WOR since it is running lean and the WOR leans the system out as it warms. CHeck for leaks, check the connections for the fuel accumulator and everything that branches off of it, maybe something got twisted just enough to cause a crack. Forget the start valve. Could be the AAV is not shutting. Take off and check. They can be taken apart and adjusted. I figure if it is not working, might as well try. I would first try the reverse of what I wrote ealier about the mixture control unit and throttle body screw.

Good luck.

David