Low RPM's in 1st

[enoloc]

Im having a weird problem with my tranny.
1998 XLT 4WD, SOHC 4.0L

When going from a stop to 1st, pressing the gas my rpms stay very low and my truck barely moves or sometimes even dies, even if I floor the gas pedal. Once i do get going, its ok, only happens from stop to first. In neutral, I can press the gas and the rpms are perfect, reverse is ok also. Ive tried with O/D off and on, tried in 1&2 all with the same results. Did filter and fluid change, no help. Can this be the tranny or something else?

 

[jimbo74]

sounds to me like the maf or the iac

 

[enoloc]

How can I test it to make sure its working ok? Ive already cleaned it.

 

[Opera House]

Sounds like two clutches for different gears engaging at the same time or one of the one way clutches hanging up. This transmission 5R55E has had problems with valve body gaskets but I haven't heard this symptom before. From a stop, in any forward gear, you are in first with the torque converter slipping. Intermediate or high clutch would have to be engaging. Does it do this all the time? Try going down an incline in manual 1 with no foot on the gas. Should be engine braking.

Strange thing. Even if the transmission was locked up, the torque converter should allow the rpm to go over 2K before stalling the engine. Putting your foot on the gas would eliminate any IAC effects. I would be inclined to think it might be an engine problem. You got to have other synptoms.

 

[enoloc]

Ok, ill try the incline, only other problem im having is the cold start problem, checked for codes got got something like fuel running lean at bank 1&2. I think the codes were p0171 and p0174.

 

[Opera House]

That would be consistant with my first thought, low fuel pressure. 98, I believe still has the rail mounted pressyer regulator. In this system 80% of the fuel goes back to the tank so engine demand doesn't have much of an effect unless the filter is really blocked, the pump is on its last legs, or there is a lot of resistance. If you have a meter and measure at the fuse, the pump current should be about 5A. Under 4A and you are in trouble. At the fuel rail pressure should be about 33# at idle, 39# with regulator vacuum hose removed. MAF, TPS, EGR, coolant and air temp sensors, intake gasket leaks could all cause these problems as well as bad plugs. Your symptoms are so extreme that I wouls expect some other codes to show up. Not worth looking at the transmission. What rpm does it idle at in neutral and in gear?