Idle rpm drops

[Bart]

Hello everyone

I've got a celica sti 1993 target edition. My parents also drive a celica, they bought it new. I compare my celica with the celica of my parents if it has some problems. The problem my celica has is that the rpm drops when it's in idle. Also when i shift and i press the clutch long enough the rpm will also drop under the idle rpm and bounce back up.

So to make it clear, it idles at 800rpm then suddenly it drops to 400 or 600 rpm and then bounces back to 800rpm. I don't hear any fan coming on so i presume it's off. I do notice that the car has this problem more in the summer than in the winter. Today was a very warm day compared to the previous weeks and today it had this rpm drop very bad.

There are periods that it doesn't do this, but there are periods that it does it everytime.

The spark plugs are changed. The mechanic at the garage said he thinks a valve is burned but also said that would be surprising because he never heard of it with celica's unless it runs on lpg instead of gasoline.
However when a valve is burned you should have loss of power, and i don't notice any loss of power if i compare it against the celica of my parents.

I've downloaded a repair manual of the 5th gen celica, and it mentioned that the idle rpm should be adjusted every 20 000 km's. I don't remember the exact amount of km, but i'm pretty sure it was 20k. My garagist doesn't have an obd2 reader so he couldn't check it.

The air filter seemed to be clean.

I also have to mention that i've got it 2 years now and it started about a year ago. Also the fins of the radiator were almost completely gone but the mechanic said it didn't hurt as long as the temperature didn't get higher then usual. At a certain point it leaked and the fan was going like crazy. So i filled it up again and bought a refurbished one. The water temperature never went higher than the middle of the gauge. So i don't think this did any damage.

Does anyone have an idea of what it can be? The mechanic said it doesn't do damage to any parts but i'd rather have it fixed if it doesn't cost a lot of money. I'm still a student so i try to fix it as cheap as possible.

Thanks in advance


Bart

edit : I also forgot to mention that the gas tank had a hole in it. I noticed it after about 4 months after purchase by accident. I never fill it up, but once i filled it more than usual and it also stood inside of the garage of my parents for a day. And i noticed some drops on the floor. So they switched it with another one (second hand tank). Could it be that there is a gasoline filter that is poluted by dirt that was in the tank they installed? Would it cause this problem?

[subspec]

Sounds like the idle control valve, clean that up and see if it helps

[Bart]

Ok, thanks. I'll take a look at that.