90 Corolla running well then

Hi guys , Tester, Keith, Rod… '90 Corolla 4AFE - 4cyl , auto, running well…without prior symptoms, now starts (4-5 times) and idles roughly (no moisture in the air) …seems to me to be fuel… I know it could be many things - but i have to travel to the car ( not much time last night) . I’m sure you can suggest things I don’t know…It doesn’t rev clean, sounds choking and very slow especially in drive/rev…not as sharp misses. Start with the fuel filter ? Can the fuel pump go quickly ?or does it go slowly. injectors? I’ll check for coil arcing tonight, and the strength of the exhaust (Cat is 23 yrs old…Vinny?) Sorry to have so little data at this time. IAC ? …Dist cap, wires and plugs are good…Thanks for any ideas, Mike P.s. a mechanic told me that in 20 yrs of his work , he only had two fuel filters be the problem…Tah


Hook up a vacuum gauge while it’s running
Perform a fuel pressure test
Perform a fuel injector balance test
Perform a back pressure test to make sure the cat’s not already plugged

Have you already cleaned the throttle and IAC?

If the fuel filter is plugged, you may have correct pressure, but very low volume

Try this.

Turn the ignition switch to the run position for two seconds, and turn the ignition switch off. Repeat this a dozen times. This will cycle the fuel pump enough times to reprime the fuel system. Now try starting the engine. If the engine runs smooth for a few seconds and then starts running rough it points to the fuel pump.


If Testers test doesn’t indicate a fuel problem, then remove the upper timing cover, turn the engine to TDC and see if the cams line up properly. If you can’t do this, at least remove the distributor cap and check that the ignitor is lined up with a vane on the distributor shaft. At least one cam will be right if this checks out.

It sounds like you have a miss though, either due to a bad plug (or wire) or a burned valve, remotely possible a clogged fuel injector. You could also have a bad coil (again not real likely) or just need a new distributor cap. I believe the coil is mated to the cap so it is not as easy to replace as in other vehicles.

Also check every vacuum line for leaks.

My Corolla is a similar vintage, 200K. I’m assuming all the engine routine maintenance is up to date. And the CEL is not on, and no codes stored. If not, do that first. Then … hmmmm … I guess the very first step I’d do is test, one by one, using a vacuum pump/gauge, all the vacuum devices and hoses for vacuum leaks. Esp if this happened suddenly. The first suspect would be that a hose that is supposed to be connected to the intake manifold has simply came loose or split. Second would be the brake booster has sprung a diaphram leak. Could be vacuum leaks in the fuel pressure regular, egr, etc too. I’d check the manifold vacuum at idle too, as mentioned above. Should be close to 20. Next I’d check for spark at each plug, then do a compression test. Then a fuel pressure test. Hopefully it is a simple vacuum leak, but in any event, you or your shop should be able to figure it out. These cars, Toyotas of that vintage, are pretty reliable, and when they break, are pretty easy to diagnose and fix.