Sometimes my car has a strange patterned idle where it surges a little bit to 1k rpm or so then the tone dies down and goes back to 800 rpm or so... It goes up and down with the same time (5secs or so) at each speed continuously (up down up down up etc....). It doesn't happen all of the time, but I'd like to know if it hints at some budding problem I'm not aware of. I'm always worried that some computerized trash or sensors are doing things I don't know how to diagnose... -- No codes are ever thrown when it does this... Thanks for any help.

 

No one has any ideas?

 

Sounds like a vaccum leak from the description.

 

Check the hoses for cracks or leaks.

 

Listen for a hissing sound when the idle goes down and you can use a garden hose to you ear, propane, or starting fluid to locate the leak. When you spray the "stuff" you should hear a slight increase in idle as it enters the intake. Did you replace something recently?

 

I haven't "replaced" anything recently, and as I mentioned it doesn't always happen. But I have taken the intake off a few times and I wondered if that may have caused this occurence. In taking the intake off I mean removing the two hose clamps and removing the maf sensor plug to move the intake out of the way to clean the throttle body and intake (with Amsoil Power Foam). I may have a chance to check for some hissing tomorrow, but is there anything specific that may be a common vacuum issue for a 95 with ~88k miles? (keep in mind that this isn't happening at the moment, but it has come and gone many times, and when it is doing it I feel like I shouldn't be driving the car). Does a vacuum leak surge up and down like I described? What makes it do that? -- Thanks for the input thus far.

Someone mentioned looking for a cracked hose... I don't have any idea which one, but I do know without looking at the engine that there is a cracked hose that connects to the throttle body. I'll have to take a look when I get a chance and report back to figure out how important that one is. Since that one is cracked I suppose other things could be rotten as well -- I have been planning to get that stuff sorted out, but have been far too busy between a full time job and summer courses... I'll have plenty of time when both are over on August 1st.

Thanks again for the suggestions -- I'll try to post back within the next few hours if I get a chance to look at the engine.

 

My last post in another thread has reminded me that last time I took the intake off I could not get the car to idle at all -- it would crank on then immediately shut off even if I tried to rev it up. Typically I could take the intake off and the car would seem to idle even better than with it on -- and I could shoot Power Foam into it while it was running. But last time I couldn't get the car to run at all without the intake completely on... I thought this may help diagnose what is going on. Let me know. Thanks.

 

By intake...do you mean air duct (the platic that runs between the MAF and the TB?

 

I am saying intake as in between the throttle body and air filter housing (the "accordion"). What else does the maf sensor go into? -- this is mentioned in my 12:06 posting. The intake manifold has never been taken off if that is what you thought I might have been saying.

 

I've seen quite a few folks here calling this the "intake" recently. This can be confusing as an intake is usually what the intake manifold is called. This would be better referred to as the air intake or the air intake ducting.

 

My 87 does this but only when cold. Once the motor runs for a minute, the idle settles down to about 750. It has a GM ZZ3 cam but that by itself should not cause a problem with a "hunting" idle.

Try cleaning the throttle body blades and the IAC. The IAC pintle may be sticking. Throttle body cleaner can be used on the butterflys and the IAC. Also check TPS voltage; should be .54V with the throttle closed.

 

Try disconnecting the MAF and starting the engine too see if it makes a difference. It will probably set a code but can be reset by disconnecting the battery. Just an easy idea.

 

The cracked hose on the throttle body is the top most hose on the passengers side. Its split longer than an inch where it connects -- I may post a picture of that area later when I go out to change the oil... -- What does this hose do and should it be replaced immediately?

 

Just went out and looked at my 95 and the top most hose on the passenger side goes into the passengerside valve cover. I would reloace this as it could lead to a vac leak. BTW, I broke a vacuum line when I disconnected this hose. WTF...oh well.

 

Yes it does go into the passenger side valve cover (I didn't take it off as I wouldn't know what it did anyway by doing so). Could this perhaps be the culprit? -- the break seems to be down the length of the connection. If I do take a picture it would probably be posted between 11-midnight est.

 

I wouldn't worry about the pic. You can feel if either end has vacuum when the engine is running. Not so sure what it does but my guess is vac. Feel the crack when the engine is running or put a dollar bill or such, at it to see it it sucks to it.

 

No harm in trying that -- I imagine spraying something on it would be the best test.

 

starting fluid or propane.