View Full Version : 1990 ST Rpugh idle/injector not firing.

09-09-2013, 04:26 AM
My 1990 Celica ST started to have a rough idle. I replaced plugs and gently sanded distributor leads, but problem was still prevelant. Started pulling injector plugs with the car running to find one made no difference to idle. The car was sitting for quite some time before bein started, could the injector just be clogged?
New to the forum, could anyone offer some insight? Thanks.

09-09-2013, 04:52 AM
Test the connector you pulled off to make sure it has signal to pulse the injector in question. If it does, then chances are you might have a problem with the injector itself. Some part stores rent out noid lights that are used to test for pulse. You could also use a multimeter. I should also add that, in case it doesn't have a pulse, that their is a wire diagram for your car (I had to check it out myself a few days ago) in the BGB that can show you where the other end of the injector wiring ends up so you can test there as well.

09-09-2013, 09:06 AM
Which injector?

Also, make sure that it is sealing well. You can get vacuum leaks through the seals and they dry up over time so if it was sitting awhile that's worth checking.

If it is clogged you could try soaking it in seafoam for awhile.

10-05-2013, 01:22 PM
Before you condemn the single fuel injector, make sure the plug stem going through the valve cover & head is not shorting the spark to the spark plug tube. I've had the problem several times on 90 Celica ST's. To test it, since you know what cylinder is having the problem, just pull that spark plug wire off the plug, but leave it sit on it, start the engine, then gradually pull that spark plug wire out of the spark plug tube. Best to do in the dark. Only spark coming out of that spark plug wire should come from the bottom of it and head towards the metal tube. If the spark is coming out of the spark plug wire from somewhere higher than the very bottom, you have to replace that spark plug wire.

I would really test this first before messing with the injectors.

david in germany
10-06-2013, 11:30 AM
If you find it is a wire to the plug it is best to replace it with the Oem one piece wire and cap set. Also stay away from Bosch plugs on the 4a-fe. The only time I ever had a stumble in mine was because of Bosch plugs.