Not your typical idle question (not ISV related)

[Sagaris]

My 1991 325i idles steadily at the right rpm, but it has an inconsistent beat to it, kind of a random blip that is hard to explain. My old Digifant VW Jetta did this as well ( which has a very similar fuel system). You cannot notice the inconsistency on the tach and you cannot hear it when you are listening to the tailpipe. It is only something you notice in the car with the windows up and the radio/fan off.

For those of you that looked at the thread title and thought "Oh great another noob, I will just tell him to clean his ISV and be on my way" you fail at reading :P

Recently I have done the following (all OEM parts): new plugs,plugs wires, timing belt , cap, rotor, valve adjustment, air filter, cleaned AFM, cleaned grounds and batt. terminals. This idle thing has happened ever since I bought the car and none of these maintenance items have had any noticable impact on it.

My thoughts are that it has something to do with the injector spray pattern, voltage output (I will have to see if the voltage fluctuates when it 'blips') or just the fact that its an old EFI design.

What do you think?

[jlevie]

How many miles on the O2 sensor? if 100k, replace it.

You could have dirty injectors. A healthy dose or two of Tecron in the gas tank may help. Or you can pull the injectors and have the cleaned and flow tested.

[Sagaris]

I dont know that the O2 sensor has ever been replaced though I will have to see if the problem occurs during open loop ( I think it does, I will check next time I drive) .

[Sagaris]

Im not normally a bumper but.....

bumpage

[E30_fiend]

is it like a: (excuse this if you dont understand)

hmmmmmmmmm-buh-hmmmmmmm-buh-buh-hmmmmm

understandable?

I think I know what you are talking about and my car has done the same thing. Always. it never effected how it drove so I never fixed it but I do have one question, what ECU or DME do you have? It SHOULD be a 173. If not, tell us which one you have.





Taylor

[SpecM]

I hate to say it, and it may just be me, but all m20 idle a little lumpy.

does it feel like a miss or like a choke? (<very subjective, I know)

[SpecM]

hmmmmmmmmm-buh-hmmmmmmm-buh-buh-hmmmmm

hahaha thats what mine sounds like!

[E30_fiend]

shit thats almost sig-worthy. Haha.

Yeah it seems they all idle a bit weird but also if he by chance got a different DME than a 173 then he may have the option of getting the 173 for the updated 1.3 motronic which smoothed out the idle.

[Sagaris]

I have a 1991 so I am going to assume I have a 173, I will have to take a look over the holiday break for the chance that maybe it has been swapped.

and
hmmmmmmmmm-buh-hmmmmmmm-buh-buh-hmmmmm

is right!

It seems more and more likely that this issue is just the old EFI system. It shouldnt bother me since the thing runs tip-top otherwise.

[nickpdx]

Mine sounds the same, as well as all of the other m20s I've heard