View Full Version : 3.4 Idle problem

08-30-2008, 12:55 AM
This just started happening this past week. Every now and then when I am sitting at a light my oil pressure stays up around 60-ish instead of dropping down to about 40 and all of a sudden the the rpm's drop from 800 or so to 600, I hear a slight knock sound from the engine, the car shakes once and everything returns to normal. I asked the person who usually helps me with any car problems what was going on, but the said that it was just an idle problem. It seems like it could be more than that but i don't know much about this sort of thing. The car is a 94 3.4 A4, any help is appreciated.

08-30-2008, 01:24 AM
Their are so many things that can cause this problem, its hard to narrow it down to one. Your not throwing any codes correct? first things i could do is check and clean the maf.

08-30-2008, 01:27 AM
I'm not sure what it might be but I know that 3.4=no maf :P

08-30-2008, 01:44 AM
excuse me guys, been drinking a little, missed the 3.4 part.

a couple ideas...

your voltage could be dropping when your comming to a start which can cause this surging effect. other things that could be at fault are 02's and the iat. i would start with what is cheapest, and even trying to clean the sensors listed.

again sorry about the maf, im deep into some yager bombs right now.

08-30-2008, 11:48 AM
Drunk posting ftw?

The SES light isn't coming on when this happens so there I don't have any codes thrown. I have been told to replace the IAC and TPS to fix a rough idle problem that i already have and I'll check the o2 sensors while I'm at it.

09-01-2008, 03:09 PM
Yea drunk post ftmfw. check back in with the results.

09-04-2008, 02:30 PM
Changed the TPS and IAC over the weekend but didn't have time to check the o2 sensors, that will be this weekend. The problem is still there but its not quite as bad. One thing that i noticed though, this only happens when I come to a stop and my oil pressure doesn't drop to 40 or so. I'm not sure if the oil [ressure dropping is normal, but just something that I noticed.

09-04-2008, 02:34 PM
well when you come to a stop the engine speed slows, and you will see a drop in oil pressure. 40psi is good, so nothing to worry about there.

09-04-2008, 09:56 PM
yeah that pressure seems about right.

09-04-2008, 10:31 PM
So, would the oil pressure not dropping cause any problems?

09-04-2008, 10:40 PM
your car is fine. youre probably seeing the rpms drop due to the ac clutch kicking on/off. totally normal

09-05-2008, 12:42 PM
You sure about that? Last time I checked, it's not normal for a car's rpm's to drop so low, then hear a knocking noise from the engine while sitting at a light.

09-05-2008, 12:51 PM
yea to me the 600 rpm does seem a little low. as for the "knocking" it could be from such low oil flow at those rpms, and causing lifter noise.

09-05-2008, 04:46 PM
such low oil flow? unless youre hitting a very low single digit psi its not low. gm cars are fine into the high single digits in oil pressure. so i have serious doubts about you getting lifter tick from that. if you have lifter tick, you'd have it all the time or at the very least on start up.

when the clutch engages its essentially a parasite on the motor, and we're talking about a 3.4 here so its not some 400hp motor that wont blink an eye at it when it kicks on so it will drop the rpms a bit. and i fail to see how 600 is bad, being as it is that you idle at 8-900 rpms anyways.

im willing to bet when it happens the lights dim for a second also, correct?

09-05-2008, 05:03 PM
yea im not saying that 600 is anything that is going to cause problems, its just a bit lower then whats normal. while the clutch may be causing the rpm drop, its for sure not the cause of the ticking. Their are so many different things that can cause a tick, its basically a process of elimination.

09-05-2008, 05:27 PM
i already told you what the tick/knock is....

09-05-2008, 06:34 PM
yeah its nothing major

09-05-2008, 06:37 PM
pressure is under normal conditions anywhere from 40 - 65 psi

09-05-2008, 09:20 PM
Alright, I'll just forget about it then, since it's nothing serious.