High RPMs on startup.

[gary rabbitt]

Hi,
Just recently my '96 started having an issue with high RPMs on startup.
First start of the day, it would rev to maybe 1200 right after start, then taper off to around 800 which I think would be normal.

Drive for a few miles, fully warmed up. Upon starting again, the RPM would go to at least 1700-1800 for a few seconds, then revert back to 'normal' idle (out of gear).

The vehicle has 162K miles, and had always run great.
I did a quick check of vacuum lines, etc and everything seems ok.
Scanned for codes last month at a shop, and no codes were shown, and the Check Engine light has not come on at all.

I was certified ASE back when CCC first came out, but never dealt with OBD type systems.

What could cause this to happen?

Thanks Gary.

 

[Snow]

Coolant Temperature sensor near the thermostat housing perhaps? If it's covered in goo, it'll never read as being warmed up, thus fast idling much longer. Are you also getting lousy mileage?

 

[gary rabbitt]

Hi Snow,
Thanks for the reply.
No, I don't think it's the coolant sensor.

In the first post, the engine would idle fine after warmup.
Shut the engine off for 2 minutes, restart, and upon starting, the RPM would go up to 1800 rpm. Not normal. After it warmed up, idle was perfect.

The problem surfaced when:
Shut off 20 min, start again, immediately high idle for a few seconds, 1700 1800, then back to normal.

My engine is spotless compared to some of the ones shown on this forum, as far as gunk goes on the engine, it is non existant. I know you can have a bad "clean" sensor, but this was not indicating a coolant temp issue.

PROBLEM SOLVED???
I was able to remedy the situation. It may be a true fix, maybe not, surprised no one mentioned this to try.

I disconnected the battery cables for their 6 month cleaning. They looked fine. This of course removed power from the computer.

Upon reconnecting the cables, the engine starts normal, and after warmup, it will start again at a lower RPM. Normal like 1000 RPM, then a second later, back to normal idle.

Fixed? As far as I am concerned there is no issue anymore.

So, for those techs out there (if there are any), was this a fix? To reset, power cycle the computer? Could a previous glitch have stored some instruction in the computer to run high on every start?
I sure don't know, but is is possible.

Thanks Snow, you are the only one who responded and I appreciate that.

I was assuming this forum was for more than installing "bling bling" mirrors and custom exhausts and wheels and aftermarket decorations.

Take care,
Gary.