1999 Corolla Le Will Not Idle - Toyota Corolla, Chevy Prizm (1998-2008)

Guest Trackrocket

Hello, this is my first post on this forum...so take it easy on me. default_smile

I am a member of several technical forums to include Ford Trucks (F250 PSD 6.0L), several Porsche related forums (I race one) and a Chevy SSR and Hummer forum (neighbor has issues all the time with his).

NOW my other neighbor has a 1999 Corolla LE with what seems to be a simple problem...

It starts and runs well, when when you let it idle, it dies. The engine seems to run real well, I checked oil levels, clean air filter, you name it and looked for a MAF...couldn't find one. I'm not a mechanic but am very mechanical...I do all the work on my Diesel truck, Porsche race car, girlfriends Jeep, the weed-whacker, the lawn mower...even a leaf blower - Haha...but didn't want to leap into replacing parts on my neighbor's Corolla.

I see an idle screw, but figure that's not the problem as it's locked by the small nut and still has the factory paint pen mark to see that it remains at that adjustment.

Should I check timing? If so, what should I look for, I have a light.

There is a sensor above the throttle body (reads something like "Sensor Vac") and one below that I can't quite read...I have unplugged both of them and worked the connectors a bit in an attempt to improve a possible weak connection...no dice. The car was a quart low on oil and I used to own a Vega that would do this if it was low on oil...added a quart, no go...

I am guessing one of these sensors is a TPS?? I don't hear the audible "click" that I look for on my 911 racer that indicates the TPS is engaging...am I on the right track here?

Sorry for all the questions, I have done a search on this issue and found A LOT of posts that discuss high or erratic idle, but none that talk about the engine just dying at idle. So what suggestions might you have for me to become the "hero" once again with another neighbor?? default_biggrin

Hello and Welcome to the forums.

You've pretty much covered a good portion of possible culprits. Here are some others that I would check out to see if you can get some things ruled out.

- Check spark plugs and plug wires. Read the plugs and see if they are showing anything unusual (heavy deposits, fouled, heavily worn, etc.)

- Check the throttle body, make sure that is is clear of varnish and carbon deposits. Could be a clogged IAC valve (Idle Air Control) - it lets air in the engine to maintain idle speed. If you kick on the A/C, the idle speed should jump up. See if the car still stalls with a faster idle speed or not.

- PCV valve and/or tubing could be completely clogged. If the PCV system is clogged, that could lead to erratic idle quality.

- Vacuum leak is also high on my list, the problem is where. Might try the old school trick of some water+detergent sprayed around suspect areas. If idle jumps, then you've found the leak.

- Fuel pressure could be too low at idle speed, not a whole lot you can do about checking that unless you have one of Toyota fuel line SST (Special Service Tools). This is a returnless fuel system, so no easy way to measure the pressure.

- Note this generation does not have a MAF sensor, it is MAP based. Also no EGR to worry about either. Timing is set by the ECM, no distributor to "slew" here. TPS sensor, can't really mess too much with that - either good or bad. Idle speed setscrews are potted by the manufacturer, I've never run into a situation where you needed to adjust those.

There are a bunch more possibilities, but the ones you've hit and the ones above are the most common.