Hi guys. Newbie ( Tom McGinnity ,Massachusetts )

Read through the posts but am not finidng a simular issue...

Start the truck and back out of the driveway. Put into drive and the engine stumbles just off idle. You can feather the pedal to get her up to speed ( 10 or so MPH ).. Then its fine. It idles perfectly fine as well until throttle is applied. Other times I might try not feathering ( putting the throttle right down per usual) and it stumbles and lightly chokes ( the sound of gagging at the throttle body ) and really bogs until your near full pedal travel ( never has actually stalled amazingly).. It then collects itself and revs fast.. this mostly occures with first start of the day or when sitting for a bunch of hours but still slightly warm.. The truck runs perfectly fine otherwise and idles smooth. Truck has original exhaust and cat...

I just replaced the cap and rotor that had some carbon tracking and about 40k on them . The truck has 126k total and has already had the intake manifold update etc.

Well cared for clean, neat, tuned and serviced vehicle

Thanks..

While I have your eyes: The fuel gauge reads dead nuts full upon start up and then bounces around awful.. after a few minutes its at 1/3 tank regardless of fuel content.. ground? if so wheres the obvios place to look? trucks not a rust bucket so I'm hoping not above the tank

Any chance the two are related?

 

I would test your TPS sensor for proper output (~0.5V at closed throttle and a smooth transition to ~4.5V at wide open throttle) to see if that is having an impact on your cold performance. Also, you may want to clean your EGR valve and MAF sensor for good measure.

As far as the fuel level is concerned, you would need to test the circuit. Here's a thread that should help:
98+ Fuel Gauge Diagnosis

 

I'll check all three items and report back.. Got little league tonight so might be a day or two. Thanks for the timely response..

PS the diagnosis on the fuel gauge looks scary

 

It's not that bad. Some of the checks do require the use of a capable bi-directional scan tool, but you can check the operation of the float when filling or draining the tank if you install some jumper wires to the proper terminals in the plug at the pump (not an easy task, but not impossible). You can pick up resistors valued from 40ohms to 250ohms from Radioshack to test the wiring back up and through to the dash for proper operation.

 

I always like to make just one change at a time per day or test drive. this is a cold only problem so its a once a day thing.. so far:

Cap - rotor.. no dice
Bought and installed new TPS.. no dice
Have ERG gasket: will disassemble and clean tonight
after that I'll clean the MAP

 

I chose to clean the MAP before the EGR last night. This moring the truck ran perfect and the engine light is out that I assumed was from the bad fuel gauge... Will report back if its a permenant repair. The tubes of the MAP were absolutely covered in what looked like black soot. The three little diode looking things were equally covered. I took that unit apart with the four screws and cleaned it with CRC MAP cleaner and a little water color brush til shiny new looking.. I was amazed. I thank you in advance for this website and the advice

picture.

 

A dirty MAF sensor (what you cleaned) can cause stumbling since it takes time for the heated elements to sense the air flow. The grayish-silver elements are what need to be cleaned (carefully) to ensure that the MAF can accurately read the air flow. Glad it worked for you!!

Just some further information. MAF = Mass Air Flow. MAP = Manifold Absolute Pressure. The MAP sensor is located near the coil/ICM bracket on the upper intake plenum.

 

Sorry.. got confused..

regardless. The repair is a full success. The MAF cleaning was the hot ticket. I thank you.

While I have your eyes: I have a 1990 SS454 pickup that does a strange stalling at idle.. Runs fine otherwise.. Should I Private Message you to see if you might have some ideas ( A good man is hard to find when it comes to these quirky dilemmas! )

Thanks again. Tom

 

On the 454, check for vacuum leaks as well as a hung open EGR valve. The throttle body base gasket is known for failing.