RPM Fluctuation

[89Supra_TurbO]

I have an 89 Toyota Supra Turbo. It has 71,000 miles and I have had it for about 6 months now. I don't know if it is anything serious or not, but after starting the car sometimes the RPM's go up and down between 650 and 1000 and sometimes lower then 650 and higher then 1000, but if u let it run it goes back to normal. Other times ill start it up and it runs at 1000 then after it warms up it drops to 650 and runs normal. I really don't know what the problem is or if there is really any problem at all. When I first bought it it would always go to 1000 rpm when I first started it then drop to normal (650) rpm when it got warmed up. But latley it has started fluctuating alot more. Any help?

[bgrieger]

welcome.

Your problem can have a few sources. The most common include vacuum or intake plumbing leaks after the airflow meter. First though, have you checked your codes to see if the ECU stored anything?

[89Supra_TurbO]

Originally Posted by bgrieger

welcome.

Your problem can have a few sources. The most common include vacuum or intake plumbing leaks after the airflow meter. First though, have you checked your codes to see if the ECU stored anything?

I don't know a whole lot about these supra's so I don't even know how. Although I had the air filter checked at my last oil change and the guy was struggling to take it off and I told him not to bother because I had just checked it. Maybe he didn't put it back on right. Ill check that tomorrow but regardless can you explain to me how to check the ECU.

[bgrieger]

in the diag block beside the fuse box under the hood, use a paperclip and jumper terminals E1 and Te1 and turn the key to the on position (don't start it though)

The check engine light will flash the code numbers out like morse code. The light flashes in .5 second intervals, with 1.5 seconds between the 2 digit codes, ie: ---.5 on, .5 off, .5 on, .5 off, .5 on, 1.5 off, .5 on, .5 off, .5on--- would be code 32. There will be a 2.5 second pause between codes if more than one are stored, and when it gets to the end, there is a 4.5 second pause and it starts the message over again. Let us know what you find (if anything).

[89Supra_TurbO]

I'll try this tomorrow and let you know.

[Jeeves]

I've seen this usually be either an air leak after the air flow meter OR a broken wire to the idle air controller. The latter results in it taking too many steps (it is a stepper motor) up or down, causing it to take in too much air at a time.

[89Supra_TurbO]

I just checked the ECU and there wasn't any codes. The check engine light just flashed on and off I waited for a minute and nothing changed. So I really don't know what to do from here .