LTCMontana

Amazing. I'm having the exact same problems and am chasing all of the same fixes. I also have an intermitent CEL.

Do you have the air box mod? Mine seemed to start having problems after i did the box mod.

kwikt

I have 2 airboxes. The modded one seems to make the hesitation more pronounced as opposed the the stock air box. It "seems" to have more low end torque with the stock one. BTW the car idles around 800-900rpm when warm and 1000-1100rpms cold. More ideas

Kevin

lsinlv

I would check the coolant temp sensor to verify it's within spec to see that you are not running too lean....also, verify you have a clean sweep from the throttle position switch...no dead spots.

using a DMM for both with factory specs is the best way.

FRporscheman

temp sensor.... now that you mention it, the normal running temp of this car is like 10 degrees higher than what it should be... but would that cause hesitation just from idle though? The car revs fine all the way up. It does lack punch. I'll check the sensor and a plug.

kwikt

Alright ... just came back from autoxing. Noticed also that when the car is run hard and up to temp and let sit for 10-20 minutes, it turns over normally but takes a little time to start. Only happens when it is warm or hot, not cold. Almost seems like starving for fuel! So now I'm thinking fuel pump or the screen in the tank. Does the fuel pump always make noisey buzz sound always. My 911 doesn't!!!! Ideas again

Kevin

RajDatta

Kevin, the fuel pump should not be that loud.
Raj

kwikt

Raj... when the car is running I can put my hand on the gas tank(under the carpet in the hatch area) and feel quite a bit of vibration through the tank. We autoxed the car yesterday without the rear carpet and constantly heard that annoying buzzing. I was wondering if someone can double check and compare my findings. I think I'm closing in on my problem. Like I said before my 911 doesn't do it neither does my 330i.

Kevin

RajDatta

Kevin, I will check mine tonight but I never remember the fuel pump to be this loud where you can hear it.
I will report back.
Raj

lsinlv

your recent posts are providing more insight, and based upon your statements about "hard hot start", and in addition to that a "noisy fuel pump", I am of the belief that your fuel pump is going bad.

you can run a cold and hot fuel pressure test to see if it is providing adequate pressure, but there are other specific tests (BOSCH) for testing fuel pump output VOLUME.

you can also perform a leak-down test for the fuel pump to see if it's internal check-valve is failing.

additionally, I was talking about the sensor the ECU uses for fueling, not the sensor that tells you how hot the engine is. coolant temp sensor (CTS) is not the same as a temperature sending unit. if the CTS gets slow, or out of spec, it will send the ECU erroneous signal as to engine temp, and negatively affect fueling. BUT, since you don't seem to have cold start issues, I would think, this is not your problem.

Neverendz

Just suggestions here, as I can't diagnose from my keyboard.

If your car doesn't lose power under heavy acceleration then your fuel pressure should be fine. I've never seen a fuel pump cause an off idle hesitatiion. Could be a first though.

Your plugs are white or light gray in color because of the additives that you have used.

Never clean a MAF.

Causes that are most likely, but not limited to:

Bad MAF- try tapping on it lightly as the car idles to see of there is a dip in RPM.
- Bosch makes a very good MAF though. You can also diagnose it by disconnecting it and driving the car. Some cars will run this way in a "limp home" mode. Others won't run at all. But you can try.

Cracked/loose air tube between MAF and throttle body. When the engine torques it can open up a split in the tube or pull any additional additonal hoses loose. Then when the engine smooths it's fine again. Also be sure that the clamps are centered and tight. A skewed clamp is a problem.

Dirty throttle plate. Check top, bottom and the back of the plate. Clean only with air intake cleaner. Using other stuff such as CRC, brake or carb cleaner will kill your O2 sensor. Don't spray a whole can in there either. Small sprays and a clean lint free cloth. Be sure there is no play in the throttle shaft. Just wiggle the linkage. While your there have someone hold the gas to the floor to see if the plate opens 100%. I've had three 951s and they all would only open about 85 to 90 percent.

Vacuum leaks. How much vacuum are you pulling at idle?

Misadjusted idle speed.

I don't know if the TPS on these cars are adjustable... If it is and it's misadjusted the computer won't know when to increase the injector pulse width when the throttle is off idle. This is also why you should never screw with your idle speed unless you use the proper method.....

Fun stuff.

, Bill

kwikt

Well, I bit the bullet and ordered a fuel pump today. Well if it's not that I'll be selling my used one in the classifieds. After researching and everyones feedback it sounds like the problem lies in pump. It's been like this for the last year and I've replaced about every sensor on the car. Oh, also I'm replacing the gas tank screen. Still open for ideas while waiting for my fuel pump

Kevin

LTCMontana

How many with this problem have aftermarket chips?

Is there any way a chip can "hiccup?"

I'm planning to reinstall my factory chip to see if there is any change.

Don't get me wrong, I'm not pointing fingers and I would gladdly purchase another chip if this proves true. I'm just trying to solve a frustrating gremlin.