Mike J

This sounds exactly like my car. Its going into the shop this morning...I have exhausted all the avenues that a shade tree mechanic like myself can do. I have checked the vacuum, looked for vacuum leaks, replaced the plug wires/cap/rotor, checked the distributor belt (its OK), removed, inspected and retorqued ALL the plugs, checked all the intake clamps, took the exhaust headers off to check the SAI ports (all fine by the way). No luck.

I will report on any results.

Cheers,

Mike

morologous

Interestingly enough, I started the car on Saturday and it exhibited exactly zero gremlins. I'm a little perplexed about it. I drove the car to the office and back (working on saturday :/ ) and it still didn't exhibit the strange behavior (the **phut** sound, the low/rough idle, CEL, any of it-- bizarro).

The only thing I did between the occurrance and the weekend drive was to disconnect and reconnect the ignition coils to the distributors. I also made sure all the plug wires were well connected. Other than that, I did nothing.

The car's still going in for maintenence this week and I'll put the questions to the service manager. Hopefully it's just a case of automotive hypochondria.

Laura

Mike,
Do you have the original dual mass flywheel?

With the miles you stated, if you do it could be signs that it is failing. The clutch operation could be working fine and as such gives no indication. But the crank sensor obtains readings from the fywheel and if those are interrupted because of wear it senses misfire, sends codes to the computer, CEL light illuminates, fault code reads misfire.

Have your mechanic read the computer and note at what RPM the misfires occur.

Jack Esposito

Mike,
I was having some missfire codes on my 96 C4S. Ran a standard vacuum check test per the shop manual and it looked good. The problem was actually downsteam from the fresh air/engine air solenoid that I hooked the vacuum gage to. The downstream vacuum unit that operates the switchover for the fresh air/ engine air flap on the engine was bad and leaking. I temporarily plugged the vacuum line with a golf tee and the problem seems to have gone away. My A/C units also doesn't cutout now under partial throttle.

Jack

Mike J

Well, just back from the shop. I have had two reputable shops look at my car and both have concluded that its the valve guides. The **phut** **phut** sound appears to be the valves not quite seating properly on the seats because they are not centered. The clincher for me was the leakdown tests...ranged from 8% to 20% which means the valves were not sealing well.

I might attempt the ultimate DYI by doing the top end job myself. I would send out the heads to get them done of course but do the assembly/disassembly. . Now where is that Bruce Anderson course when you need it..... ?

If I do it the rebuild I will document it for the list.

Cheers,

Mike

Mike J

Hi Laura,

Thanks for the response. Yes, I have a DMF on the car and I can understand that it can screw up the crank sensor and create fault codes. But this car also idles a bit rough (a slight shudder) and there is definitely a backfire **phut** short of noise out of both exhausts, more on the right. The leakdown test was pretty bad (worse was 20% on one piston). Oil consumption is about 900 miles/liter.

The misfires occur immediately as you clear them.

I will raise the issue with my mechanic (which by the way is Weissach here in Vancouver) and see if he look at it.

Have you seen a slight backfire noise in the exhaust at idle becuase of the DMF failing?

Cheers,

Mike

Mike J

Wow, that sounds like a win-win situation. I am not so blessed (so far) in that I doubt if any of the local Vancouver shops would do this. I also thought I could strip the engine down to the bare block and have it done...no one in this area is willing to do that either. They want total control of the quality. I can understand that since if things go bad it could be lots of $$$.

Not sure what my next steps are yet.

Cheers,

Mike

Laura

Mike,
Did he hook up the PST and run the car at idle and check RPM' readings as the misfires occur? This is very important for diagnosing this problem.

www.hergesheimer.com

morologous

Update: Took the car in for it's health and wellbeing check (separate from it's MD inspection). Let me tell you, I was nervous as a cat. Several hours later the call came in: Nothing to fear. Mechanically nominal in terms of operation.

I'm going to pursue the low idle issue with the dealer and see if there's anything he can tell me about it, but barring that I'll just try to clean up the ISV. Truthfully, the idle has been pretty good since I reseated the ignition coil connections.

I guess I'm just a little bit of a hypochondriac in this matter. I think I'll still take it to get a second opinion, but at least the initial results have been positive.

Adrienne

I'll chime in since I just had my guides replaced. Your symptoms all sound familiar. My car had a rough idle and hesitated a bit when cold. At operating temp, the engine was not completely smooth. My oil consumption was up at ~700 miles/qt.

Now with the top end rebuilt I have not added a single quart in over 2000 miles, my engine is smooth when cold, at idle, and operating speed.

A complete valve job could run you $500-1000, so if you can do the tear down yourself, or at least parts of it, you stand to save a lot of money.

trojanman

I think she meant $5,000 to $10,000... don't mean to put words into your mouth, Adrienne, but I need to meet your mechanic if that's his price!

My top end rebuild (including new exhaust valves and non-OEM exhaust guides) was just under $5k.

Good luck.

ventoGT

Adrienne--where in the world have you been? Thought you may have dropped off the earth or something! Anyhow, hope that I don't have to swallow that bill anytime soon--good luck with the issues Mike--hope that it ends up being cheaper than expected!

Adrienne

Maybe I should clarify -- valve job alone (meaning sending the heads to a shop for honing, guide replacement) is $500-1000, but the complete top end rebuild is $5k. My valve job was $800 or so, but that was just the head work with no valve replacement necessary. The tear down, parts, clean up, etc added up to plenty more than that, say, and order of magnitude higher.

Where have I been? Well, driving my car, of course!! After being 993-less for 5 months, I had some making up to do!! New top end, new suspension, new paint. I have a 2005 993 now.

trojanman

HAHA... you sound just like me, Adrienne. It does feel like driving a new car. I did the LWF/clutch, top end, and suspension (H&R coil-overs)... which set-up did you go with?

Adrienne

I did the M030 springs and HD shocks. It's super-duper low now by comparison. The paintwork is amazing - complete re-paint! As you can see from my avatar, I painted the grill and removed the rear bumperettes. Beautiful! But, don't want to go too far off topic. I'm planning to post my car's transformation pics over the weekend. Stay tuned....