Stumble at take off

88911coupe · 08-14-2006, 07:59 AM

I have had a problem on my 88 for as long as I can remember and it's starting to really wear on me. For the record, it's an '88 3.2 with about 160k on the clock. It is definitely using oil too quickly but this problem started well prior to the increased oil consumption and it runs fine otherwise and idles about 850 steady. Here's the problem...it seems to stumble off the line in traffic. It's as if there is very little power at the lower rpms when I pull away from a stopligt as if the slightest thing will cause it to stall. I recall a few years ago something about there being a hose near the airbox needing to be connected and I am sure all hoses are connected as designed. Has anyone ever had this problem? I also vaguely recall Steve Wong saying someting about this issue on 3.2's but I've never heard back from him on my inquiry.
Any suggestions?
TIA

2.7RACER · 08-14-2006, 08:20 AM

Buck,
Has the mass airflow sensor ever been replaced. This is the part that measures the air into the motor. The key part is a potentiometer inside that wears out and sends false or no signals to your ecu.
Plenty of info on this site and the tech forum on how to test and replace it.

Steve W · Steve W's Garage

Hi Buck, sorry for a lack of response - I try to answer all my emails, but there are so many that sometimes I miss a few or they get blocked by my spam filter. If so just try and resend the message again. As for bucking, renew the insides of the air flow meter by moving the wiper up or down the shaft to track on a new resistive surface. At 160k miles, there are sure to be signal dropoffs expecially at the first 20 degrees of wiper movement. The hose by the airbox that should be checked is the vacuum line to the fuel pressure damper on the right side fuel rail. Dripping oil can cause the rubber hose to swell and cause a vacuum leak to the fuel pressure regulator hose, as they share the same vacuum line. An air leak here will cause the fuel pressure to be too high just off idle and at light loads, creating a rich bog situation just as you crack the throttle. Also, you'd want to make sure your head temp sensor is within spec.

ruf-porsche · ruf-porsche's Garage

Check this link

Stumbling at low rpms-'88 3.2 Carrera

88911coupe · 08-14-2006, 09:14 AM

Thanks everyone for the quick replies...I now have some good things to check. No problem Steve...I was just hoping someone knew about the thread where I thought you'd talked about this issue specifically. I can imagine how many calls/emails you get.

stlrj · 08-15-2006, 06:28 PM

How old are your ignition cables?

Goth · 06:56 PM

On my 84; I had what I would have originally described a "Just off idle stumble". After finding the problem, I would now call it something like a "Just off closed throttle stumble".

It used to be embarrassing when starting out in traffic. I thought everybody must be saying "THAT GUY HAS A PORSCHE & CAN"T EVEN DRIVE A STICK!"

Anyway... Toward the back side of the throttle body, there is a micro switch that should just barely click when the throttle is closed, and/or just cracked open. Once I adjusted that, all was fine.

Edit: fyi..It was staying on past closed throttle which tells the DME to try and keep the RPMs @ idle speed.

88911coupe · 08-16-2006, 05:49 AM

The cables are about 1 1/2 years old but this was happening before and after I replaced them.
Doug, could you give me a little more detail about the switch you are talking about? When you say "backside" of throttle body are you saying the side nearest the firewall or the side towards the back of the car? Also, how did you adjust it or is that obvious when I look at it?
TIA

stlrj · 08-16-2006, 08:04 AM

Quote:

cables are about 1 1/2 years old but this was happening before and after I replaced them.

Regardless of how new your cables might be, it is still quite possible that some arcing might be present at the distributor cable connectors during low rpm high load conditions as in taking off in 1st gear.

So it might be worth smearing some dielectric grease inside your cap connector boots to see if that helps.

Cheers,

Joe

Goth · 08-16-2006, 07:07 PM

Quote:

more detail about the switch you are talking about? When you say "backside" of throttle body are you saying the side nearest the firewall or the side towards the back of the car? Also, how did you adjust it or is that obvious when I look at it?

It's on the side nearest the firewall.

I think you could adjust the throttle plate position & then readjust the idle speed control. I believe there is a spec for the plate gap inside the throttle body, but not sure what that is (anybody know?).

I could not find any other adjustment for the switch (other than bending or grinding something). The plastic switch looks like it has 2 plastic pins going through the metal part it's mounted to, and then melted over like a rivet. In my case, I found the switch would move up and down a little bit. When I pushed it down, it would then rev up smoothly, but it would not stay like that for long. After a short drive the switch would move back up. So I pushed it down and super glued it to the metal mounting point (I know... kinda cheesy, but it worked).

88911coupe · 08-17-2006, 12:17 PM

Thanks, that's very helpful. at least I have a place to start.

Goth · 08-17-2006, 07:30 PM

Good Luck & Keep us Posted...

stlrj · 08-18-2006, 05:05 PM

Your mixture might be set too rich which could also be causing a rich bog and stumble.

Joe