Intermittent Hesitation

[Jay87]

Hey folks,

Car is an '87 325is, stock so far as I know. Every once in a while, the car hesitates on acceleration. At one point, cruising down the freeway, I jammed the gas pedal and the engine nearly stalled before catching (this happened very fast). It was almost like I killed the ignition for a half a second.

My first thought is fuel - the car has an inline fuel pump that was replaced last november by the previous owner, but that whines incredibly loudly.

The second is spark, though I'm not sure why this would fail intermittently.

I figure I will replace the fuel pump and filter first and see what happens. Where can I find a cheap fuel pump?

Thanks,
Jay

[Sagaris]

When I first bought my car, It hesitated like yours and I went through and replaced:

Oxygen sensor
Coolant temp sensor (to the ECU)
Spark plugs
Distributor cap + rotor
Spark plug wires


each item improved the hesitation slightly but the Distrbutor cap +rotor and the sparkplug wires were what completely cured it. They were original @ 187k. You also may have an intake leak but Im betting on ignition components.

[2.5-12]

this same thing was happening on my 87iC, it turns out my 02 sensor was completely gone and the car still wasnt throwing a CEL For it,

new sensor and no more hesitation and almost dieing on the highway

if that doesnt fix it, do everything that Sagaris mentioned, its good preventative maintenance anyway on an older car and well worth the initial cost.

[sohc12vm20]

Sounds like the 02 sensor needs to be replaced..

[rabbitude]

It may be the O2 sensor, but I had the exact same problem which turned out to be a vacuum leak which was causing the O2 sensor make the car super lean and the car was starving for fuel

[Jay87]

Thanks for the replies. I'll look into an O2 sensor, I don't believe its been replaced. The previous owner said that most of the ignition components were replaced, but I keep finding reasons to doubt his work...

[Jay87]

I know I might get flamed for this, but how about a universal O2 sensor? Waaay cheaper than an E30 specific one, unless I don't know where to look.

[iwantspeed]

I had a similar issue

I replaced quite a few things trying to diagnose it.

cap
rotor
plugs
I didnt replace the wires but I plan on doing that soon.

air filter
fuel filter
oil change
oil filter
various vacuum components
o2 sensor
main relay
ecu relay
o2 sensor heater relay
crank position switch
main engine ground strap
fuel pump
coolant temp sensor(blue base goes to dme)


mine was fixed by swapping out the ecu with a stock ecu with a stock chip.
I assume there was a cold soder joint, a broken joint or something of that nature.

the car still has an occasional long cranking to get it started.

[iwantspeed]

also found this

http://www.r3vlimited.com/board/showthread.php?p=2031014#post2031014