Weird symptom, please help analyze

[areznik]

Hey guys, here is something weird happening with my Q45 '94 115K. When in park my idle is lower than in drive?! According to the tachometer I have about 600-650 in drive and about 500-550 in park. Also, when I shift the gear from drive to park I don't see the usual slight jump in RPMs. What it does is just reduces the RPMs by about 100 or so. I suspect that IAC probably does not give enough air but wanted to hear your thoughts? I don't know what proportion of air does IAC supply in drive and in park. Are there any other differences in air induction between park and drive. By knowing these I can probably identify the "weak link".

Has any one had it before? Last time when I changed oil I put synthetic Mobile 1 and performance Mobil 1 oil filter. These are the only changes that I made for the last 5 months or so.

One more thing, about a week ago I added BG44K and did the same thing two months ago (I am a big fan of this product after my long story with durty fuel system last spring).

Your ideas and suggestions would be greatly appreciated,

Andre.

[elwesso]

Andre

We had a meet today and I forgot to call you.. Some WILD cars out there today...

Anyway I would start by cleaning your IAC.. Get a new IAC gasket.. Its supposed to 10-15% duty cycle on the IAC at park, and probably like 20-30% in drive...

I bet its sticking.. Clean it out, and then if necessary adjust the screw to 2.5-3 turns out....

[areznik]

Wes,

I cleaned the IAC today and it was not dirty at all because as far as I can remember I cleaned it about 8 months ago. The problem still does not go away and idle in park sometimes is as low as 500 rpm. In drive it is usually about 550-600rpm. Other than that the car is fine (knoking on wood). Do you have any other suggestions ... ?

Andre.

[maxnix]

Did you adjust the idle control screw? Should be between 2.5 and 3 turns out from fully seated.

[areznik]

Yeap, I did. The IAC screw is 3 turns out. This is very weird since I NEVER observed this kind of behavior of my Q. I order air and coolant hoses from Joe and I will change them next week. Hopefully, it will solve the problem (i.e. maybe there is an air leak). Although, what really puzzles me is why the rpms are fine in drive and not in park??

Andre.

[areznik]

Hello everyone,

Wanted to post a solution to this problem. In one word - PCV. My PCV was really clogged and that little pin inside did not move at all. Last weekend I did the plenum job, replaced both knock sensors, most of the underplenum hoses, and the PCV. Then drove 2000 miles to Florida and no problems whatsorever.

All the best,

Andre.

[elwesso]

Good deal Andre!

Those things can get dirty and stick fairly easy.... good practice to clean or replace sometime (only like $10)