Malibu Starting Problem

Have an unusual starting problem my mechanic can't fix. Here's the background on my 2000 Malibu, 3.1L engine:
When engine is cold it starts fine and operates well. Starting problem shows up when trying to restart the engine when it is still hot. It then has trouble starting and if it does start it runs very roughly. Putting it in gear will make it stall out. After engine cools enough it will restart without any problems and run fine. As long as you don’t shut off the engine it will then run normally. Once when I put the AC on during normal operation the RPM would not go above about 2500 RPM.

Mechanic checked for fault codes and there were none.

The following things have been replaced within the past 6 months:

Fuel Pump
Fuel Filter
EGR Valve
Plugs

Anybody else have similar symptoms that they were able to fix?

I have an 01 malibu with a similar problem not as bad though. Have you had any trouble with the coolant, an intake leak? An oil change might also be helpful. :banghead:

Thanks for your reply - the only one so far.
In response to your questions - no coolant problems and I do regular oil changes.
How would an intake leak cause the symptoms I've described and where would such a leak likely be found?

Try the fuel pressure regulator on the fuel rail. I had long hard starts when the motor was hot and then stumbling when it finally started. I pulled the vaccum line off the fuel pressure regulator and smelled gas vapor. Starts much quicker now with the new regulator. Beware of a bad IAT sensor harness & plug assembly on your 01 Malibu, it seems a lot of them go bad and cause the Transmission to shift hard in to gear and hard when upshifting. Don't rule out bad Spark plug wires, they gradually go bad and should be replaced at around 50K miles no matter how the look. Try different brands of gas too, I found Shell regular gas gives me the best starts, fuel mileage and smoothest idle.

Fuel pressure regulator was my next target since that seemed to solve similar problems on other vehicles posted here and another web site. Just so I understand the mechanics here, what is physical malfunction in the fuel pressure regulator to cause the problem and make the car hard to start when hot?

Far as I can tell there is a rubber diaphram in the fuel pressure regulator that can no longer hold vaccum because of a hole or rupture. This causes the fuel pressure to be erratic and not hold the correct pressure in the fuel rail when starting. I smelled gas at the vaccum line when I pulled it off the fuel pressure regulator, a proper working regulator won't let gas in to the vaccum line and will hold pressure.

Thanks for helping me to understand what's happening, but I have a question regarding your response. If a hole in the diaphragm is the problem, why would it only show symptoms when I'm starting the engine when it's hot? Wouldn't it cause problems when I'm starting the engine cold or in normal engine operation after it's started?

I’ve seen bad engine grounds cause similar issues. Grab a set of booster cables and ground the engine to the body next time it won’t start. It’s a quick check that can at least rule it out if it’s not the issue.

have you checked the catalic converter. when the catalic gets hot it will restrict the air going out the exaust the synptoms you mention sound just like that take it to a muffler shop and have it checked out i have seen this problem on some cars

About the muffler with time the catalic will get clog you have to remove it or if you want to save money take off the three bolts with a long steel tube poke the inside until no more comes out when you think that all came out turn the car on for about 10seconds then turn it off (it will make the left overs come out) part two change the tempstate to a lower one (meaning) the one that opens in less temp. Part three bleed the coolant there is a line that run like it front of the oil cap follow it torwards the belt and there a bolts (with the car off and when it hot ) open it slowly and let the air or bubbles come out (when coolant come out close the bolt back