I'm stumped. My 97 lt1 engine is staying at a 2500 rpm idle (sometimes it will be at 1200rpm) until I come to a stop. Just recently, I had to replace the TPS which was putting off a low voltage code. Since then this has happened. I also noticed a drop in my 0-60 times from 5 sec to 5.86 sec. I have an obdii scan tool, but all things appear funtional. Any ideas? Could a bad fuel filter cause the problem?

 

I am thinking vaccum leak.

 

I do not see any obvious vacuum leaks. The cruise works perfect, which does often work with vacuum. What is the best location to draw a vacuum for testing purposes. Could a marginal IAC cause this issue without setting off a code?

 

It may be your IAC. My friend had a high idle problem for a while and he had a oil leak at the back of the intake manifold which i would think be a vaccum leak also. We put new gaskets on and bam his car idles at 650 now.

 

Had a new clutch put in about 2K miles ago. At 70K miles the pivot bolt broke and allowed the clutch fork to rip things up. Anyway, the mechanic said that things were bone dry back there, so it may not be that particular vacuum leak. Thanks for the ideas. After I get a good idea of the possibilities, I will start to test for each one.

 

I'll be more specific on the symptoms.

It has alwas idled at about 800 rpms, but would idle down to 1200 rpms if I was slowing down to a stop, at which point it would drop to 800 rpms.

Now it idles at about 1200 rpms, but idles at 2500rpms if I a slowing down to a stop, at which point it would drop to 1200 rpms. But, about 25% of the time it idles idles down correctly.

Today it has been missing and bucking, but without setting off the ses. Fuel economy has been in the 24+ mpg range, and yesterday it was running fantastic. That's why I was surprised this morning that it wouldn't and gave a tps low votage code. Started fine after putting in a new tps, but now have these new symptoms. Even disconted the battery inhopes the ECU would reset.

 

update:

Checked vacuum lines and have no leaks, based on pulling vacuum off of driver side intak manifold.

Cleaned th throttle body, IAC passages and IAC pittle end. Extremely crudy.

Started car and idled at 800 rpm, and drove fantastic with loads of power for first five minutes. But it is now a an even higher idle than before. It also now bucks, makes a sparking noise out the exhasut and gose o-60 in 6.9 sec (vrs a normal of 5 sec and 5.85 sec prior to the cleaning). Also, the OBD still reports a TPS error, but this is now the third TPS placed in the car, so I'm sure it can't be that.

My thought is that the IAC is so meesed up, that it's letting too much air through. If no one else has a better idea, I will be replacing the IAC.

 

Sounds Like If Your Tps Is Adjustable That It Needs Adjustment

 

They all are stock tps's.

 

if your car is "bucking", i would check the o2 sensors, as for just the high idle, when you replaced the tps, did you put the right vacuum tube in the right spot on the intake? check the vacuum lines on the passenger side of the intake manifold...i did this when i changed my intake manifold gasket, and it turns out that was the cause. the tube with the grey end goes under the one from the egr...i think

 

1. Started car this morning and let idle. 800rpm, tps @ 0%, warm idle vacuum is steady 30KPaA (about 4.25psi).

2. Rev engine up and down a few times, settles at 1200rpms, tps @3%,vacuum same.

Turned engine off and on, went back to first readings.

IO2 sensors checked out.

 

Not feeling good about the vacuum reading, I redid the teat with a different gauge. I tested the vacuum off of a drive side vacuum port and had a steady 20psi. This while the idle was still messing up.

 

i have the same exact problem. i checked for vaccum leaks, the iac, tps, etc. i heard that it may be map sensor related. when i turn on the ac on everything is fine. what happens when u turn your ac on?

 

It has gotten so bad during the last three test drives,that I won't even try to test drive it anymore. I did notice that the a/c clutch kept cycling on/off every few seconds. It has never done this before.

Could bad gas cause a problem like this|? During my last test drive, the car seems to "ping" out the exhaust duing acceleration.

I wasn't able to get an IAC today. By the way, my IAC tests out okay. I'm just hoping that a dirty IAC is not moving the plunger where the ECM tells it to, perhaps allowing too much air bypass causing a lean out duing acceleration and total confusion to the ECU.

 

I replaced the IAC, and it ran even worse.

I changed the fuel filter, when water came out of the line. I then emptied the tank since bad gas seemed likely.

Car restarted fine, idled fine. Took it for a drive, but it is still bucking with a bad tps value. Checked the TPs and it shows 3% at idle. Put the original tps in and it shows 3% at idle. If I turn the tps clock wise about an 8th inch, it goes to 0%.

I plan to elongate the holes to adjust the tps.

Any ideas why the sudden problems. Can water in the gas cause these types of problem? The car ran perfect prior to the gas fillup.

Thanks