I have a 1995 F-350 with the I-6 that I love very well except that it has a problem that has baffled two mechanics, two Ford Dealers, and is not getting much better. It starts and drives fine when its cold. When it warms up in 10-15 miles and I stop such as at a stop light it begins to choke down and get a miss then die. The Ford shop installed a new TP Sensor, Coolant Temp Sensor, EGR Valve, and I have installed new plugs and wires along with a new rotor bug and cap. Now that they have done all this, the engine doesn't die, but sits and surges high then low when it's warm and in gear with the brakes applied. The trick is it has to be warm then and in gear as if stopped at a stop light waiting for the light to change.

Now the Ford dealer is telling me that I may need a new transmission, which just sounds odd to me especially being as it's the inline 6 with EFI and a C-6 transmission and is an otherwise basic work truck with 101,000 miles. Any ideas as to what could be the problem? I am at a total loss and so are the mechanics that have looked at the truck.

 

Do a compression check and check the vacuum at the MAP sensor. If the vacuum is too low the problem you described can be results.

 

How do I do that and where is that located? I rebuilt the vacuum lines to the vacuum chamber and couldn't find any others under the hood. What sort of vacuum should it carry?

 

They pulled codes?

 

That's the thing that has them all confused. There are no codes to pull. The engine started having problems described above and never once triggered the check engine light or anything - just idling rough under a strain when hot. I get it from the dealer Monday morning and am going to start looking at it again myself to check the map sensor and vacuum line that feeds it as suggessted by 5_LabsDown and I talked to a friend at a tranny shop and he doesn't believe it's the transmission either, but something so profoundly simple that the Ford mechanics are overlooking it. Another suggestion was to disconnect the coolant temp sensor and check for a bad wire or bad connection (they replaced the sensor along with the tp sensor and egv) and have had it for three weeks (two at one dealer and a full week at our "largest Ford dealer in Oklahoma" with no results. We did, however, rule out a burned valve because it seems to affect the ignition and the truck runs lean. When we changed the plugs they were the original plugs that came with the truck and what was left of them was frosted white.

 

have the shop run a backpressure test.

 

OK. I'll be talking to them today and ask if they have or if they will then let you know the results.

 

Have they checked the IAC? It may be gunked up and either needs to be cleaned or replaced.

 

I'm assuming that the IAC is the Idle Air Control and if it is then yes. We installed a new one of those first before doing anything else and it made no difference. They said the dying was from the stuck EGR Valve, but they can't say what the surging that's happening is caused by once it warms up and is driven for several miles, which is why they're saying that it's in the transmission. I think that's their way of saying they're tired of trying to find it and now that they have our money they want it gone.

 

Keep on them to get this fixed. Also, did they ever find any stored codes?

 

No codes at all until they began fiddling with the egr valve. It never once tripped the check engine light either.

 

Man, thats rough... Ever look into the possiblity of it being a fuel problem. Could be a bum fuel pump, or could even be o2 sensers. My mustang had a pretty similar problem, and it turned out to be the fuel filter.

 

They checked the pressure and said one is low, but shouldn't be the problem and the other is kicking out 70 pounds and oxygen sensor is very responsive. Puzzling isn't it?

 

I would like to take a sec and thank everyone for their help in advance. I've gotten a lot of good suggestions that even the Ford dealer hadn't considered. I'm going to get the truck home and follow up with the advice I've gotten here because every time Ford does something it costs mega bucks (already almost a thousand bucks I didn't have and still not fixed). I wish I'd known about this forum from the beginning.

 

I know this is a few days late, but maybe a fault gas cap?