Hello all.
I have a 1998 Monte with a L36 that has been experiencing poor fuel economy and hesitation at WOT. The best description is the car feels heavy and lazy
The problems all began after I had the fuel injectors professionally serviced and cleaned. The fuel injectors themselves have been ruled out since they have been flow tested while on the car.
Since then a number of items have been checked and replaced...
Fuel Pressure
PCV Valve
K&N Filter
MAF Sensor Cleaned and Swapped Tested
Emission EVAP to Throttle Body Vacuum Line
Upper Intake Manifold and Gasket
Lower Intake Manifold Gasket
Upper & Lower Radiator Hoses
Coolant Sensor
O2 Manifold Sensor
Valve Cover Gaskets

I'm not getting a SEL, but my scanner has my LTFT stuck at +16.4 at idle or when I lift off the throttle. At WOT they drop but usually nothing lower than +1.5. This looks like a vacuum leak, but 2 different shops have said I have no leaks.
My STFT are around +16.4 to about +20.3 at idle.
The other thing I've noticed is that my Throttle Pct. and Throttle Volatge on my scanner seem to be low, especially at WOT. I swapped my Throttle Position Sensor, but I have the same problem and same low numbers.
Any ideas would be helpful.
Thanks.

 

Who serviced your injectors? Maybe take it back to them and see if they know whats up because it didn't do it before they touched it. I imagine that you have checked all the injectors to make sure they are seated properly in the intake. A good way to check for vaccum leaks is to spray a little starter fluid around hose connections and you could spray it around the injectors to see if air is getting sucked in through them. If the starter fluid gets sucked into the engine through a vaccum leak, the idle will change. Just some thoughts.

 

It could be a vacuum leak, you'll have to excuse my distrust with mechanics. Your O2 sensor could also be fouled - most likely from the injector cleaning.

 

Well,the car was serviced today and my CEL(P0171) problem was fixed.
The Vacuum Ball under the fender needed to be adjusted and bad PCV O-ring need to be replaced, but the damn +16.4 LTFT remain. My STFT are back at 0 at idle and WOT.

I should have written in my 1st post that my CEL came on yesterday and up to this point there was no CEL. I've had the 16.4+ LTFT at idle for a few months now with no CEL.
This is the problem that I cannot pin down.

 

Perhaps the throttle body gasket is leaking. Or the EGR gasket. Or any connection of the MAP sensor, LIM, fuel pressure regulator. Are you just going to bring it to another mechanic or are you going to fix this problem yourself?