Hesitation accelerating from stop...

[jdSHO94]

Hello All,

I have been using the search function trying to dig up everything I could about others who have experienced similar issues, but so far none quite fit the bill. Its a 1994 MTX with 255K on the clock, and after completing the first round of work that I have done lately, I have a hesitation taking off from a stop- the engine hesitates and pops back through the intake, but only below 1500 RPM- past that it runs beautifully. The issue does not happen every time, if I am really gentle with the throtle and accelerate very slowly it does not happen. I have been doing A LOT of work prepping for a cross country move, so I will start with the list of what has been done:

valve cover gaskets and plug tube seals,cam sensor and crank sensor, spark plugs and wires (motorcraft plugs and denso wires), cam seals, crank seal, and of course the timing belt and tensioner. The O2 sensors were also replaced a couple of months prior to this.

After all this was done is when the issue started. Since then, I have tried diconnecting the MAF and running the car- same issue. Unplugging the TPS also has no effect. I subsequently replaced the fuel pump and it still occurrs, only below 1500 RPM. Removing the vacuum line from the FPR makes no change either, and I also went back in and replaced the intake manifold gaskets just in case one was damaged during the initial work. This issue is driving me crazy, and I really want to have this issue repaired before I leave in a few weeks. I would really appreciate any insight you all might have. :thankyou:

 

[AREA 91]

Check for codes and report back to us.

 

[SHOdded]

Did you make sure the rear VC gasket is seated properly and has not rolled? That could cause a leak down onto the cam sensor and cause problems. I'd also check the plug wells again to make sure they are dry/oil-free.

 

[jdSHO94]

Thank you for the prompt responses. I reconnected the battery and completed a test drive then came home and pulled the DTC's as requested-

KOEO
111
122
219

KOER
538
536 (forgot that step)

I have verified that there are no leaks from the valve covers, cam seals, and oil wells, I was able to get the car on a lift a week after oil seal replacement to look it over top to bottom and verify that there were no oil leaks. The 219 is the code that interests me the most...

 

[rubydist]

when I read your initial post, I said to myself that unplugging the tps having no effect is a bad thing, because unplugging the tps makes the engine run badly. then you posted a tps code (122). that must be fixed - the tps is a very very important input to the pcm (more important than it should be, imho). you have a bad wire or connection problem on the tps circuit.

the 219 says the spout circuit has a problem and timing is fixed at 10*. it could be as simple as the spout jumper being missing or dirty connections, but usually it is in the wiring harness somewhere. that also must be fixed, because you have about 2/3 of the power you should have due to the fixed timing.

I would check for engine compartment grounds and make sure they are all in place. its easy to have missed one with all the work you have been doing. then I would check carefully to make sure there are no places in the wiring harness that look overheated or otherwise damaged. if you don't find anything there, you may need to start ohming out individual wires in the harness to see where your issue is. I have had wires open in a harness that looked perfectly fine, so sometimes they are hard to find.

 

[TankII]

Even though you replaced the wires, you might still have a bad spark plug wire.

TankII

 

[jdSHO94]

Thank you for the input everyone. I will be trying to do some pinpoint testing (if I have time after work) this week and hopefully I can track down the source.

 

[DeepPower]

How did everything work out? I just read this thread, one possibility is oil in the plug wells.

 

[jdSHO94]

My apologies for not posting the resolution, things are still crazy for me right now. After all was said and done, it ended up being one of those 3 week old spark plug wires! I wound up acquiring one of the AC Delco sets from Rockauto and replaced them in the garage- problem solved. I never did get to the root of the codes, but that can wait until after I have made my move to SHO Cal Thank you all for the input!