high idle on start up
 

I thought I seen this before but for the life of me I can not find the thread.
Anyway I just did a complete gsl-se swap into my 85 gs swapped over the cars entire wiring harness engine to tail lights I buttoned up the engine Monday and it fired right up but its high idle is 4000rpm drops down to 3500 rpm and stays there I only let it run for 2 to 3 min and it never drops please help.
This is a bone stock gsl-se 168k on the clock brand new fuel lines filter and pump and tank brand new o2 sensor everything else has not been touched thanks in advanced for the help

are those 2 to 3 minutes the only run time it's had since the engine install? if so, it's certainly not enough time to do a thorough check for vacuum leaks. i would start there.

A vacuum leak would cause a inconsistent idle or rolling idle wouldn't it

And yes this is the first time since the install

vacuum leaks can do all sorts of weird things. high idle is one of many ways it can manifest itself. it may turn out to be something else, but it's fairly easy to check as other ideas roll in.

Thanks

Clutch switch.

Nope - normal for an -SE.

The -SE uses a thermowax pellet to operate the secondary throttle plates to act much like a choke on the 12a engines. The net effect is that when you start it from cold, the gas pedal should be pushed WOT only once, and then released. This positions the throttle rod on a cold-start cam which increases initial idle speed to roughly 3k RPM (or so) in order to heat up the engine more quickly. As the engine heats up, hot coolant flows from the water pump to the thermowax pellet and back to the block - melting the wax pellet in the device and allowing the throttle to return to 'normal' idle position over time. This process takes as long as the engine takes to warm up, and driving the car is what allows the secondary throttle butterfly rod to gradually slip off of the fast-idle cam and back to normal idle conditions.

I would let it cycle through and make sure it does what I described above. If, after 5 min or so the throttle returns to a nice 800rpm idle speed - that's what it should be doing. If it never comes off of high-idle condition, then you need to start troubleshooting the thermowax system and coolant lines.

LongDuck, what about the clutch switch? If you push the pedal in and out one time while it's doing its high idle on startup, the rpm will come down to a more reasonable speed. My brother's GSL-SE did this.

Just one push is all it takes. I figured the clutch switch sends a command to the ECU which makes the BAC function a certain way, or something... and it was repeatable. I did not like this feature at all due to the cold gel-like oil being forced through everything and potentially bypassing the "bypass" inside the oil filter letting contaminates back into the bearings.

The above is one example of why I don't like EFI. I prefer to control the idle speed directly. Makes me feel more "in tune" with stuff. :)

On a fresh install, I'd be suspicious that the throttle cable is a smidge too tight... but I'm not SE-literate.

Thanks for all the help after checking it out the cruise control cable was to tight causing the butterfly's to be open adjusted the cable and 800 rpm nice and smooth

Longduck is correct. My idle starts at 3k, drops down to about 1200, then eventually down to 850.

Glad you found the root cause.

For those interested, I've never been able to offset the -SE high-idle condition by using the clutch as you've mentioned. I don't doubt that it may work, but never had it happen in my experience. Maybe others can chime in to confirm this, but I don't remember reading anything in the FSM about bypassing the high-idle with that, either.

I wouldn't be too concerned about high idle at cold start simply because more damage is done through poor oil pressure on startup (cold start then idle with little pressure to any bearings) than high-idle driving pressure to everything as quickly as possible. Mazda - in their infinite wisdom - likely factored this out when they designed the system.