Mystery Problem

[IceHammer]

Ok guys, I'm having some trouble diagnosing a problem my bird is giving me. Symptoms:

- After a few trips (approx 1 - 10 startups) the car shifts to a persistent high-idle, 1100+ rpms, varies, have seen it get as high as 2300
- Occasional low idle when it isn't high idling, ~600 rpms
- High idle issue disappears after battery disconnect for ~1min
- Occasional stall during idle
- Occasional rpm drop then surge then settle while idling
- Occasional 'hiccoughs' while under load, very similar to misfire if it isn't a misfire. Have experienced this 1 time each at 4000rpms, 3300rpms and 2000 rpoms
- While cold, very light touch to throttle causes rpm drop then it catches itself
- No check engine light

So, based on this, I replaced TPS and IAC valve. Idle quality improved considerably for a short period of time after the new IAC was installed, but now its back to its old tricks. Throttle body and IAC hole got a good dousing with carb cleaner as well.

As far as I can tell, the engine is running much too smooth to be mis-firing, but I don't think thats off the table yet. First time any of these issues happened I was replacing the water pump and I bent on of the tabs that sticks into the coil backs, maybe 30 degrees off true. Bent that back and it didn't appear to be broken. Maybe this is the cause somehow?

Anyone have any ideas on what causes a high idle when throttle input and air input should be good? Comments are appreciated.

[Jbarton34]

Re: Mystery Problem

U mess with the coolant temp sensor for the computer have had numerous problems with them giving power surges and poor performance issues otherwise check wiring n the tps circuit and tune up did a huge favor for the sputtering problem u mentioned above
also run a can of sea foam through the tank if u dont already that stuff works numbers on cleaning injectors
also 1 more thing to check is ur crank an cam position sensors those are close to where u were workin with the water pump may have got some coolant in the wiring
i hope that this can help u in some way ;)

[Meatyshells]

Re: Mystery Problem

sounds like you have an air leak

[IceHammer]

Re: Mystery Problem

Ok, so I've found that these symptoms possibly point to a vacuum leak? I've sprayed some carb cleaner around and haven't caused the engine to change its idle one way or the other. Problem is I don't know which hoses are vac lines. Anyone have some kind of diagram of this?

[Choppers]

Re: Mystery Problem

one is going to the throttle body

[flamingchicken]

Re: Mystery Problem

did you spray where the intake manifold bolts to the heads??

there is a line going in to the rear of the intake from the power brake booster, one on the fuel pressure regulator (drivers side of the fuel rail) some coming from the passenger side that is used by the vent system. also the map sensor on the passenger side of the intake, under the cowl.

[Rob Bell]

Re: Mystery Problem

Also hook up a vacuum gauge to see if you have low vacuum. That would indicate if there even is a leak. If the vacuum line tests don't work out, I would suggest looking again at the IAC. You said that for a while the idle improved considerably. Did it go back to normal? You could have gotten a bad IAC. It would be hard to diagnose though, w/o a scan tool to see if the IAC is actually working. When my IAC died on my old car, it just died and it had a steady high idle with no code. Yours could be intermittent. Also, you may need to check the wiring. If there is a break in the wiring it would cause the IAC to work intermittently.

[IceHammer]

Re: Mystery Problem

did you spray where the intake manifold bolts to the heads??

there is a line going in to the rear of the intake from the power brake booster, one on the fuel pressure regulator (drivers side of the fuel rail) some coming from the passenger side that is used by the vent system. also the map sensor on the passenger side of the intake, under the cowl.

Now that you say map sensor it reminds me of something. Last year when I bought the car it had a horrible misfire which ended up having a root cause of a leaky fuel pressure regulator diaphragm. Anyways, point of the story is that during the diagnosing of that we took off the MAP sensor and played with it.

First time this newest high idle thing happened was after I had disconnected and reconnected the battery, first time since playing with the MAP. While looking for the cause of the high idle, I noticed the MAP was not fully screwed into the manifold. The screws were backed out maybe 1/2" so I put them back in thinking nothing of it.


1. Could I have somehow broken the MAP and the engine didn't notice until disconnected the battery and forced a reset?

2. Can a bad MAP cause my symptoms?

Other questions:
If I'm in neutral / park and press the brake pedal to the floor, upon release the engine revs up a few hundred then settles back down. Is this the proper behavior? I'm wondering because maybe theres a sign when the brake vacuum assist isn't properly working.

Stumbling low idle then high idle (in that order) issue seems to crop up soon (few minutes) after a hard accel, 3500+ rpms. Is there something in terms of a sensor reading that could be doing some sort of reset if the vacuum goes too low (thinking messed up MAP here)?

Thanks for all the input guys, i appreciate having you to bounce ideas off of.

[mrbako]

Re: Mystery Problem

this doesn't sound like a vacuum leak to me. prob an ignition module prob.