Hello from Central PA...Need help with Idling issues!!

[srossman03]

New to forum and I need some help with my 1999 Tahoe. it has 5.7L v8 and a few weeks ago it started to idle poorly and had a smell of gasoline while in drive when sitting a red light. Then it started to miss badly and I barely made it home. I just bought this in February and I found out that the previous owner removed the bulb for the check engine light. Well I replaced the plugs, plug wires and put new fuel filter on. Still the same but then it started to take a long time to get the engine to start and still having same issues with idle and smell of gasoline. So I then replaced the cam shaft position sensor and this seemed to correct the problem with slow starting but still had the rough idle and smell of gasoline. I drove to Autozone and had them hook scanner up and it gave me P0300 code(multiple cylinder misfires). I then replaced distributor cap and rotor and no change. But now it was hard to start after the engine was warm and was shut off. I would have to hold gas pedal to floor to get it to start and once started, it would still idle rough and smell of gas. I then replaced coolant temp sensor and now still have rough idle and smell of gasoline still. Any ideas???

 

[07burb]

:welcome:

I'm going to rename your thread title slightly andmove your thread with the hopes it gets more exposure for your issue. :waytogo:

 

[lesterl]

Bet your FPR ruptured inside the upper intake plenum, pull the plastic bonnet off the throttle body, open the throttle by hand and look down inside to see if you have any "washing" of the carbon inside the intake, if you do it is basically dumping raw fuel into the inside of the intake.

 

[Murder n Mayhem]

Would do thorough TBI clean. Does your idle vary more when vehicle not moving & has heater\ac on? More than when the heat\ac is off?

 

[srossman03]

Idles the same regardless of the heater or AC being on. WOnder why Chevy putt he FPR under the intake plenum? Grrr I will attempt that this weekend, weather permitting. Should I but a new gasket set as well? Kinda always strapped for cash and don't want to spend unnecessary $ if i don't have to. Also hoked a cheap scan tool up this afternoon and got -30.5 readings on both Short term Fuel Trim banks 1 and 2? Any ideas?

Thank you in advance for your help.

 

[srossman03]

What do you mean by a thorough TBI clean?

 

[lesterl]

the negative fuel trim is telling a story. I would definitely look down into the intake to see if it is washed...

 

[srossman03]

I took the upper intake manifold off yesterday and I am guessing the fuel pressure regulator is the cause of all my problems. The lower intake was bright shiny aluminum under the regulator and I assume it must have been leaking fuel. Will replace today once the local auto parts store opens and will report back with my results. Thanks lesterl,07burb and Murder n Mayhem for your help along the way, you have saved me a lot of time and $!!:happy160:

 

[srossman03]

Still no relief

Well I put new fuel pressure regulator in and I still have the P0300 code and rough idle. Anyone have any other ideas?

 

[lesterl]

Can you read your fuel pressure? Hows the plugs/ Cap / rotor/ wires? Still got some major negative fuel trims.... Did you pressurize the fuel system with the intake open to check for leaks?

 

[srossman03]

Just replaced cap, rotor, plugs and wires and fuel pressure was 54-55 at idle.

 

[Mthebull]

From experience with the same issues on my Tahoe the coolant temp sensor was the culprit. I know you already replaced it but I went through two before I got a good one. This little part is often overlooked and will cause you to throw a bunch of money at your vehicle with no success. When this sensor is bad your vehicle will idle very rough, with smell of gas, just like yours. Also some brands include the little wire harness as sometimes these go bad as well. theres a video on you tube where someone uses a scanner to check the coolant sensor readings. Good luck

 

[srossman03]

Just took out the new coolant temp sensor and checked resistance on it and the old one and they both seem to be working so I am not sure that is the problem. How do I do a compression test? do I need any expensive tools? Not sure what it could be at all, maybe it's something mechanical with the engine?? it does have almost 200 K on it, I put less than 5 K a year on it but previous owner said he did regular maintenance and used AC Delco parts. It was fine on my way to work a few weeks ago and then after work it started missing and carrying on and hasn't been the same since. I have seemed to have fixed all the other issues except for this miss and P0300 code.

 

[lesterl]

54-55 sounds alittle low, shure you didn't get the oring twisted on the FPR? Do you have the original Poppets or the newer MPFI update? Was the housing on the injector manifold cracked?

 

[srossman03]

I don't think the o-ring is twisted and they are still the original poppet injectors. I am running a can of Seafoam with this tank of gas and the negative fuel trims have gotten considerably better but still have a rough idle???? And the SES light even went out for a short time but is now back on again. I haven't checked fuel pressure since replacing regulator. What should I be looking at for readings?

 

[lesterl]

"The Fuel System Pressure



60-66 PSI (Pounds per Square Inch)Vent the fuel tank vapors by loosening the fuel cap. Position the ignition switch and the A/C system in the off position. Install a fuel pressure gauge to the vehicles fuel pressure valve.Confirm that no leaks are present, and with the key on, engine off verify the PSI reading on the gauge."

Per Autozone.com repair manual......

 

[lesterl]

You could also have a fowled up spider injector (the orginal poppets are notorious for plugging up.....

 

[vbu2c5]

Just went through the same issues with my 1998 2 dr Tahoe. The washing of the intake manifold is a bad sign and mine had the same thing. Replaced the old poppet style injectors with the new style from Delphi and it idles like new now. Also replaced the throttle position sensor, air idle control and the MAP sensor. The idle was staying around 1100rpm's for a little bit when I was coming to a stop and it was probably the AIC sensor but I went ahead and replaced them all.

There's a youtube video on how to replace the old spider injectors with the new style, not a 30 minute job but not out of the realm of a shade tree mechanic either. I wouldn't wait to long to do this as I have heard of some horror stories about the fuel igniting under the throttle body and creating a mess or a big fire. Good luck.

 

[srossman03]

I do think I need to replace the spider. I have run a can of Seafoam through fuel tank and got a little better and then ran a can of B12 Chemtool through fuel tank and the CEL will go off when not in city driving but as soon as I am back to stop and go driving, CEL back on and rough idle again. Oddly though, only getting P0302 code now. Any how, Thanks everyone for your time and input but I guess I have to start saving for a new injection spider. My only complaint on these things is if I'm paying $300 for a part and it is going to take me a weekend to install it, you would think the warranty would be more than 1 year.????:help::help::help:

 

[vbu2c5]

If it's hard to start and you've already done spark plugs, wires, distributor and fuel filter I can almost guarantee you it is the spider injection which was a bad design to begin with. There is a fuel regulator on the old design spider injector that looks like it should have a hose connected to it but that's where it pulls its vacuum from. That tube is where it is shooting out fuel and it washes the intake right underneath it, not a good thing! The smell of gas is a tell tale sign. You will be amazed how good it runs after replacing it, I know I was. Fires up instantly now and idles smooth as glass. Don't wait too long if possible.