flat spot at 2250 rpm, 2.5L manual

[StinkyTwinky]

I own a 2000 OBW 2.5L manual with 115k on it. Just bought it and performed a full tune up which helped it run much better. I noticed a bit of a hesatation/stumble around 2250 rpm. Mostly in 3rd but also in 2nd and a little in 4th. This happens during accleration most of the time but sometimes not at all. I can live with it but would like to fix it because it leads to jerky shifting. Any ideas?

[Saint J VT]

Does your Check Engine Light on the dash light up when you turn the key to "on" but do not yet start the engine?

If the instrument light-bulb is good, then the second question is, does the Check Engine Light ever come on after you have started the engine?

[cardoc]

A little "hickup" could be caused by a number of things. Clean your throttle body, IAC motor, double check that the ignition wires aren't arcing to a close ground, make sure the air filter is clean and your fuel filter is clean then see if it still does it.

And yes, go ahead and scan for MIL codes or any codes for that matter and see if anything comes up.

[StinkyTwinky]

The light does come on with ignition but has never come on since I bought it in june. Air and fuel filter are new. Replaced some old fuel lines too. Plugs and wires are new. Cleaned throttle body around plate but did not remove it. Iac(idle air control?) I can check that later as I am in the middle of timing belt change and ran into some frustrating issues. Won't run right at all. I posted another thread on it. Will check for codes later too. Thanks

[StinkyTwinky]

Thanks car doc. You were right. The IAC was gummed up and sticking. After a good cleaning the problem seems to be gone. Later this year I may remove and clean the throttle body.

A big thank you to all of the people who take time from their busy days to help others out. I have used many tips from this website to help fix my problems.

[cardoc]

When you remove the throttle body, have a replacement gasket on hand. You may or may not need it.

[StinkyTwinky]

Oh yeah, she is shifting way better. So very happy to have that fixed.
Why was it so gummed up? Maybe valve cover ventaltion or something? I fixed quickly in the dark so can't remeber where that tube went.
Having all the parts and tools for the job is a great idea. I live out in the county so learned that the hard way.
BTW: I like your supercharged subie. Looks like one h*ll of a sleeper!

[cardoc]

Your engine's crankcase ventilation system feeds air in and pulls air out. When it pulls air out it also pulls oil particulates with it. The higher the pressures in the crankcase, the more oil gets fed back into the intake. The PCV hose connects to the air filter box so the oil particulates pass through the IACV and through the throttle body and over the butterfly plate.

Hot metal surface, cooling carbons. It sticks. Then hardens when it cools. Builds up on the surfaces a little at a time until it causes a restriction to movement.

[StinkyTwinky]

Dang it! I spoke too soon. The problem is back but not as bad. Wonder if the IAC is going bad. Seems to be worse with the defogger on. I will keep messing with it but the car still runs so not a huge issue. This is not my year. Most everything I have been fixing lately has more problems down the road. Grrrr

[cardoc]

Rear defog or front? The rear creates an electrical load. The front runs the AC creating an engine load.