Problem Starting After Car Is Warm

[bcnvegas]

Can anyone help me? I am new to the forum after looking for a solution to my son's 1993 Lexus GS300. My son's car just started this problem of rough starting sometimes. The car starts best in the morning or when it has sat for a long while. the problem becomes consistant when the car warms up and then turned off, then wait for about 15 minutes or more and then it is very difficult to get started again. I have to rev the accelerator to get it to start, then it idles rough and eventually it will run and smooths out some. Sometimes it takes several tries and several minutes to get it to start. I took it to My mechanic who opened his own shop after working for Toyota and Lexus. He told me that the error code pointed to the Idle control valve failing. $450 part plus labor. I had it changed, got the car home then attempted to start it 20 minutes later - SAME PROBLEM! Took it back to the mechanic, He had the car several days (was able to duplicate the problem), He took the thottle body apart, checked and cleaned it along with clearing the computer and drove it around some and said he could not duplicate again. One problem that he could not figure out that started happening was the engine Idle when first started when cold will idle around 1500 rpms and will eventually go lower after running awhile. (He knows that this is not right, but does not have an explanation for it) He wanted my son to drive the car around after the throttle body check over. Guess what? Problem still exists! Drive the car home and let it sit for 15 to 20 min. and it won't start. Note: the starter cranks the engine, but you have to pump accelerator to attempt to get it to start. Mechanic did check fuel pressure and says it is good. It is hot here in vegas now, and I don't know if temp has something to do with it, or is it a vapor lock, etc...

parts replaced within the month before this problem occured:

Nipo plugs, new set sparkplug wires (lexus), lexus rotor, timing belt, waterpump. these items were done for 90k miles service. fuel filter I changed myself with a purolator after market replacement. I wanted to post this on toyota forum for the engine is the same as the Supra 2JZ motor.

[Mick24]

Has your Mechanic done a fuel pressure test ??

The Fuel Pressure should be approx. 38-44 psi with the engine running and with the engine off,the pressure should not drop below approx. 21 psi after 5 minute's.

If the Fuel System does not hold at least 21 psi with the engine off - start looking for problems with the following:

Fuel pressure regulator.

Leaking Injectors.

Check Valve on fuel pump outlet passing,allowing the System pressure to fall.

Hope some of this help's you pinpoint the Problem.

[bcnvegas]

Has your Mechanic done a fuel pressure test ??

The Fuel Pressure should be approx. 38-44 psi with the engine running and with the engine off,the pressure should not drop below approx. 21 psi after 5 minute's.

If the Fuel System does not hold at least 21 psi with the engine off - start looking for problems with the following:

Fuel pressure regulator.

Leaking Injectors.

Check Valve on fuel pump outlet passing,allowing the System pressure to fall.

Hope some of this help's you pinpoint the Problem.

                                                     

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:D My mechanic checked the fuel pressure and the check valve portion and it all checked out fine, following is the fix: Good news! Got my son's Lexus GS300 back yesterday and it does not seem to fail like i originally stated. I waited till today to post because I wanted to see if it would start and run fine. My son got it back yesterday afternoon, we drove it, let it sit while hot, then started it-seems to run fine. He drove it some last night and went to work this morning and no dreaded phone call yet of any failure. Time will tell, but it looks good so far. Here's what the Mechanic found: The car is a 1993 GS300 with the straight six. He started from the beginning forgetting everything he did before and checked for all diagnostic levels that he could. Interesting thing he explained was that being that this car is a 1993, Lexus does not share some of its diagnostic code info. The car again showed no error codes, but after the car warmed up it would be very difficult to start, Idle would be around 1500 rpm when cold started in idle. This mechanic started his Mechanic school working on the Supra in 1993 while at Toyota. He got this Idea to fool the diagnostic computer and enter the data saying the Lexus was a supra with the 2JZ engine. (says its the same) when he did this a status log revealed that the throttle sensor position sensor which has an Idle contact swith integrated in it was stating that the car was not in the idle position when the car was actually in idle. To give some background on the TPS and what it does or effects I checked a great website called: http://www.autoshop101.com/ where they explain that the TPS engine mode; idle, part throttle, wide open sensed, air-fuel ratio correction, power increase correction, fuel cut control are things it affects. the Idle contact switch was the part that was out of whack. He made the adjustment to show that the Idle sense was correct when in idle-the rpm went back to 700 rpm in idle and the car seems to start every time. The Mechanic says that somebody had to change the sensor position throwing it out of spec. (now only the Lexus dealership) did any work on the thottle body when they changed the spark plug wires. Now I asked if the Idle control valve that was replaced was any good, and he said that it was bad. (I still question that answer since the problem was still present after it was replaced) If it was bad in conjunction with the sensor out of adjustment then the computer must have been making adjustments to muddy the situation. (He reminded me, there was an error code in the beginning that pointed to the Idle control valve that left after he replaced it) So, It runs now and lets hope it stays that way. That website i mentioned previously explains things with toyota's. I hope that this will help someone else. If the Mechanic was telling the truth about fooling the computer that it was a Supra engine of the same year, maybe you can have your mechanic use the Toyota adapter and info and see if it shows you more on your car. Otherwise you have to go to the dealership and trust that they know what they are doing and that they are "honest". I was told that cars from 1995 or newer by law had to reveal there diagnostic info to mechanic outside of the dealership. Thanks for your help and input. this is a great site for people like myself.