HELP; Infrequent bumps from idle

[BhndTheWheel]

Hi All. I'm a new member (see my intro in appropriate forum).

I want to send a big thanks to Dudesky for the post on "E36 common faults". This information is invaluable and you are to be commended!

I posted the following message on a yahoo group and thought I'd seek feedback here:

Every now and then my car will skip or jump a bit as I accelerate from
a traffic light. I will try to describe this the best way that I can
because it's not happening often.

The 'bump' feels like it is from the transmission or engine. It's
almost like the engine mount is loose and that it is going to seperate
from the car, or that the transmission is going bad. When I described
it to my BMW tech (a 20-yr BMW-only expert recommended in an online
BMW forum for his honesty and fair price), he says it's not the trans.

The problem is it's happening so infrequent that I can't demonstrate
it to him (a couple of times in a day and every 5-6 days). This is
very scary to me. I'm committed to this car so it has to be resolved,
whatever it is. I appreciate any feedback or similar experiences!

[c1apton]

I'm puzzled by your description bump? Do you mean a miss - like a cough or sputter in driveability?

[Dudesky]

Thanks for the compliment, and welcome to UB.c

Do you mean the engine rpm drops abruptly, like it hesitates, causing the car to shudder? Some things to observe: when does it happen? When the engine is cold or warm? During humid/rainy conditions? The description is kinda vague, maybe more details might help

[BhndTheWheel]

I'm sorry guys. You are correct in your guessing though. C1, it is exactly like you said, a miss like a cough or sputter; but isolated to the engine area. Dudesky, it happens on a cold engine and from acceleration from a traffic light or stop sign. I'll have to notice the RPM if it happens again. There is no "check engine" light or anything diagnostic showing in the dash. I thought it might be the engine mount, fuel filter or poor quality gas/low octane?

[c1apton]

I'd start with a bottle of injection cleaner in the fuel at fill up and a chek on your air filter for starters. AFTER that tankful has gone through, if problem still exists then I'd go next to a basic tune up - plugs, fuel filter before throwing parts at it at random

[BhndTheWheel]

Good deal. Thanks!

[STROKER]

I had this happen to my 92 325I . I just replaced the clutch and all and while I had the intake off, I replaced "ALL" the hose's and the boot from the TB to MAF and all the fuel lines. And the problem is GONE! Also Clean the ICV while you are in there . You would not believe what a small crack in a hose can do..Even if the hose looks good REPLACE THEM!!!! It will make a BIG DIFFERENCE

[BhndTheWheel]

I'm sorry, excuse my ignorance. I'm learning this as we go along here. Please translate TB and MAF. I'm committed to learning to do as much as I can myself, time & skill permitting, but I am a novice.

This happened again today and I gotta admit I'm freaking out. I'm afraid to have it diagnosed cuz I just got taken for over $500 for a radiator replacement (due to plastic housing on top?) but I really can't devote time to this until the weekend.

I attempted to accelerate to beat a red light. Upon making it through the light and a left turn to resume acceleration, the engine or trans hesitated and the RPMs dropped from 2 to 1 each time it happened. This is from a cold engine and going a fairly low speed.

[witeshark]

MAF = mass airflow sensor

[BhndTheWheel]

Thanks Witeshark. Someone just suggested to me in another forum to replace "throttle position potentiometer", which sounds like the same thing. Is this something I should attempt myself?

[witeshark]

I think that would be the throttle position sensor. Where they are placed can vary a bit.