: rough idle, no codes, rough start



RickyHenry
08-07-09, 03:32 AM
Hi all! My 99 STS is exhibiting strange behaviour. Sometimes at idle, the RPMs will quickly fluctuate between around 400 - 1500 RPMs for no reason. Often it sits at a steady 550.

When I go to start the car, it sometimes needs to crank for 10-15 seconds before starting. Other half of time, the car starts up very quickly with little effort. Sometimes, I will crank and turn so long, my battery loses its juice then I need to jump start the car.

Some things I have tried:
Cleaned all fuel injectors.
Replaced fuel rail
Replaced spark plugs
Replaced plug wires
Replaced crank sensors
Replaced oxygen sensors

Some of the above was for other issues, but now the only remaining issue is this weird idle and starting intermentent issue.

Any thoughts about resolution? Thanks for consideration.

Ricky
M

My 99

Submariner409
08-07-09, 08:20 AM
Clean the throttlebody and Idle Air Control passages with rags, a toothbrush, and Throttlebody Cleaner.

Check the Fuel Pressure Regulator by starting the car and removing the vacuum line from the FPR nipple. Any raw fuel in there ?? Not good. If that looks OK, buy or have a shop test fuel pressure with a gauge attached to the fuel rail test fitting. 41 - 45 psi, running.

Fuel filter - a hex and a quick-connect fitting, under the driver's side frame rail at the rear door. Careful - 5 oz. of raw gas in your face.

Are your plug wires hooked up in accordance with wiring the diagrams posted here and elsewhere ? It's very important.

stoveguyy
08-09-09, 10:39 PM
excessive cranking will flood the engine. how does it run when you do get it to fire? a wild idle rpm could be due to an intake leak. could be the manifold gaskets? or maybe the plenum gasket between the throttle body/manifold?

Ranger
08-09-09, 10:57 PM
It's a '99. He doesn't have a plenum. That is on the 2000+'s.

RickyHenry
08-12-09, 07:11 PM
excessive cranking will flood the engine. how does it run when you do get it to fire? a wild idle rpm could be due to an intake leak. could be the manifold gaskets? or maybe the plenum gasket between the throttle body/manifold?

I just bought a new fuel pressure regulator last night, hoping to put it in tonight. The car runs fine at some times, but other times, maybe 40% of the time when I stop at a light, it will fluctuate between rpm's from about 450 - 1500 rpm back and forth quickly then settle down.

As well, the car will start right up with no problems sometimes then the car will all of a sudden tank many cranks to start up. it's odd really to me.

I'll let you know if the FPR was the culprit soon hopefully.

RickyHenry
08-13-09, 08:38 PM
OK, i put the new Fuel Pressure Regulator in. Problem disappeared. =D