1998 Lexus ES300 puzzler

I recently had an accelerator valve replaced in my Lexus ES300, 1998, due to couldn’t start. Car would turn over, but go off as soon as I removed my foot from accelerator. Now, car is behaving similarly, in that it seems to not be feeding gas and when I’m driving it will start to lunge and sputter and lose rpms. As long as I’m going it won’t go completely out, but if I have to come to stop it would. So at stop, I put in park and rev up rpms, then really step on the gas when I go and it’s fixed…won’t happen again for a few weeks to a month, but happens consistently. Check lite does not come on and mechanic is stumped. Thoughts?

If revving the engine fixes the problem for a few weeks, I would suspect the idle air controller or throttle position sensor. These can go bad and not trip the “Check Engine” light.

Thank you greatly for this tip!! I will check with my mechanic.

If your mechanic isn’t using a graphing scan tool (or, a graphing multimeter) to examine the voltage patterns of the sensors (tps, iac, O2, MAF, etc.), s/he is doing you a dis-service and is not finding the cause of the problem(s).
At this time, and mileage (average of 120,000 miles), the MAF (Mass Air Flow) sensor, and iac (idle air control) valve pintle and passage, and throttle body (plate and bore) should be cleaned with (inexpensive) products available from any auto parts store. This is to remove the oil and carbon deposits brought into the air intake tract via the pcv valve (vacuum).
The pcv valve should be changed (cheap). Sometimes, the particular Brand of pcv valve has to be used because the after-market pcv valve might have the wrong air flow.

Be sure that you are using the octane of gasoline specified by the car maker. If you don’t, THAT can cause performance problems.

I called my mechanic and he said he replaced the idel air controller. He said he has never replaced a throttle position sensor. My car is a '98, but it only has 65,000 miles on it. He did clean whatever is the pipe or hose that connects with the accel valve. I will ask him about your other questions. He has thought a possibiilty is that one of the 6 coils is bad or going bad, but my emissions people here in CA said I probably wouldn’t have passed if that was so. Also, they said I only have 3 coils not 6 on a '98…which might tell me something about my mechanic. My mechanic says cartalk has referred customers to him…Buz in Costa Mesa?

I’m confounded that your mechanic has, “never replaced a tps (throttle position sensor)”! I get the impression that he is just parts changing and not doing much (any) actual troubleshooting.
The online sites (Auto Zone and Advance Auto Parts) say that 3 ignition coils, and 6 ignition coils are required! Either way could work. It’s just a matter of ignition coil drivers. A look at the engine will reveal if it has 3 two-plug ignition coils, or 6 single plug ignition coils.
If one ignition coil is suspect (from the DTCs …such as, P0301) it can be swapped with another ignition coil. If the DTC changes (to, say, P0302), you, then, know that it was that ignition coil which was misfiring.
There are ways to test sensors with a scan tool or a multimeter. Can your mechanic do that?

I will take your suggestions to him. He said he could not see which coil without the engine check lite coming on and he did not just want to guess that that was even the problem, since it could happen from so many things. RE/TPS, he was just saying that he has never had to replace a TPS, I think indicating that my milage was too low for that to be suspect? I will ask about the scan tool or multimeter…