Does this sound like a vacuum leak to you?

[jonah111]

Hey everyone,

I’ve been trying to help my sister with an idle issue on her 1997 850 na w/ 220k miles, but have not been able to figure it out. When cold, the car will start & idle fine. As it gets warmer, a low or fluctuating idle will appear at a stop. Sometimes it goes away when the car is shifted out of D and into Park. The car drives fine but will idle around 450rpm when at a stop light- sometimes it will stall, but starts right back up. It also seems to be running rich or has a clogged PCV system- black smoke from exhaust when sitting idle. OBD reader shows code P1507 What I’ve done so far:

Cleaned original IAC
Replaced IAC twice with junkyard parts
Replace throttle position switch
Cleaned throttle body
Check for vacuum leaks w/starter fluid

Would a severely clogged PCV system cause these issues? How about the coolant temp sensor? Right now I’m thinking that there’s some sort of vacuum leak in the PCV under the intake manifold.

Thanks for any help

[vjaneczko]

A clogged PCV would (a) cause smoke to come from the dipstick tube and/or (b) inflate a balloon – both when idling, of course. Don't think any part of the cooling system would cause rough idle - but I could be wrong.

Have you checked the spark plugs?

[jblackburn]

Black smoke = unburned fuel = too MUCH fuel.

Doubtful a vacuum leak, as those cause too much air and a lean code from the O2 sensor.

The coolant temp sensor is a good bet, and cleaning the MAF sensor would also be a useful step.

[jonah111]

Sorry, forgot to mention- I also cleaned the orignal MAF and replaced it with one from a running parts car. Spark plugs were also replaced early in this process. The Lambda symbol light is also on- front O2 sensor was replaced about 5K miles ago.

I also threw on the cam position sensor & fuel pump relay from the parts car and replaced the fuel filter for the heck of it.

[jblackburn]

That means the O2 sensor is mad at the fuel mixture too, but maybe the computer is getting a fluctuating reading from the ECT. Usually this would cause a CEL for that...or at least I got one. But it took it about 2 weeks of running weird before the light actually came on.

If you've got a parts car, swap that sensor out. If it suddenly works OK, I'd buy a new one and replace the thermostat at the same time.

[jonah111]

Any reason that a bac ECT sensor could cause a P1507 code? Is there anything else to check for P1507 other than the IAC motor?

thanks