Ok, so i bought this thing for $500, the CEL was on and the typical door ajar light.

When driving at about 35 mph, the engine will start "bucking" unless you either get it up to 40ish mphor manually shift in to 2nd.

I read the codes and all 4 were o2 sensor codes, so i replaced them and did plugs (bosch platinum)and wires as well. the CEL is out and the problem is conciderably better, but its still there none the less. Any ideas?

PS, it seems to do it more after it reaches operating temperature.

 

If the vehicle was driven in the 35MPH area for the majority of its life, the TPS is probably worn causing a DEAD spot in the variable resistor. I had this issue on my 1983 Mid-Sized LTD. Wore 2 of them out by driving the majority of the time in the 45MPH range. This would cause a bucking issue when trying to maintain 45MPH. Anything below or above was OK. The DEAD spotbasically is tellingthe computer to stop fuel delivery. So every time you hit the spot, the engine gets no fuel and bucks (spits and sputters). The way I found mime was to disconnect the TPS and drive the vehicle to see if the problem has gone away. If you do this there are a couple of things to remember.

1. This will set a code for the TPS.
2. Since the TPS is not connected, the computer doesn't know what position the throttle is in so don't tromp on the gas, it willstall.
3. The engine should idle and run OK, just take is easy and get it up to the problem speed to see if it is gone.

 

Thanks. I was thinking the tps may be an issue also,but wanted a 2nd opinion. ill try what you said and see what happens.

 

I've actually seen a Dealership rebuild a 302 in a 1984 Crown VIC for this issue and put the old TPS back on. They wonder why they still had the problem. I explained the above to their Customer whileI was waiting on my Ranger. The Dealership Service Manager and ACE mechanic told the Customer I was full of it. The Customer wanted to verify if what I said was true, so he tried it. Wa-La...problem solved. The Customer was livid after finding out that his $1500 rebuild could have been solved by a $27 part at the time.

 

Funny story! Itsamazing how dealerships want people to believe that they are the only ones that know anything, and everyone else is a hack.

Anyway, so i went to run some errands this morning, (havent tried the tps thing as of yet) and the van stalled on me. I start it back up to find the CEL is backon. So i come home get my code reader out (same one autozone uses) and it gives me these codes:

P0135- Upstream Heated Oxygen Sensor Heater (HTR 11) circuit malfuntion Bank 1
P0141-Downtream Heated Oxygen Sensor Heater (HTR 11) circuit malfuntion Bank 1
P0155- Same as P0135 but Bank 2
P0161- Same as P0141 but Bank 2

These are the SAME codes i got that made me decide to change all 4 O2 sensors. Now i didnt reset the computer because im not sure how on these, but i did erase the codes with my scanner,but im not sure if that actually makes the computer re-learn the new parts. But if it thinks that the 02s are bad it will run like crap too right? And wouldnt the TPS give me some sort of code if it was bad or had a "dead spot"? What about the MAF sensor, doesnt it affect the fuel mixture as well and could be setting off the O2 codes? (my airbox lid is broken so it doesnt securely fasten)

 

I've never had a faulty TPS set any code. The DEAD spot is a true reading to the computer. It's a 0 resistance reading which to the computer is basically an IDLE condition meaning give less/no fuel. The MAF could cause the problem, but it seems it would normally be all the time at any speed. However, you can clean the MAF sensor with a Q-Tip and alcohol. I've seen numerous MAF's replaced due to just a dirty sensor. The MAF sensor can also get oil on it if you are running an oiled filter such as a K&N. As far as the O2 sensors go, FORD uses PRE-HEATED sensors. These have and additional lead to them that heats the O2 sensor so that the sensors can start working before they get heated up via the exhaust gasses. There must be a common per-heat lead to these for them all to clock a code. Look for a chaffed wire.I'll see what your results are before letting my brain run amuck again.

 

I decided to go to the junkyard and get a MAF sensor instead of paying $200+ at my local parts place, changed it, no difference. I looked at the TPS and it looks to have been changed recently. ( The previous owner was also trying to figure this problem out)

Is the TPS adjustable on these? or is it an adaptive learning system? I dont see how to adjust it by back probing the wires if it is adjustable.

Also i was paying close attention today, and it stumbles just of idle, at 25 - 35 mph, and at 55mph. at 55 if i turn o/d off it runs normal. 25- 35 mph i have to either speed up or drop into 2nd. Just off idle it will stall occasionally too. The stumbling is accompanied by a 3-500 rpm drop.

On the bright side, no CEL today.

EDIT-
Was just thinking, it better not be something stupid like a pcv valve, that would be a little embarassing [sm=smiley7.gif]. although i would be happy.

2ND EDIT-

PCV valve still rattles, so im ruling that out. Unhooked the tps as you said, and drove it, i got a lot better throttle response, BUT it ran down the road at 35mph all by itself lol, and still did the problem im having, So im ruling out the TPS also. 2 MAF sensors, same problem, ruling those out. Only thing left that i can think of (other than replacing sensors one by one) is the fuel filter, but ive never had one only give me problems at certain speeds.

 

well it wasnt the fuel filter. if i bring the rpms up to about 1200 while holdingthe brake in drive, the van starts bucking like it does going down the road. Im starting to get way too confused and about to take to a shop or the junk yard.

 

Well, sorry to hear nothing worked as of yet. I hate what I call "MICRO-GREMLINS". I just picked one up yesterday afternoon. My 2000 Taurus has a 200 RPM surge while driving. Turned the A/C off to make sure it wasn't the compressor cycling on my. Next thing to do is drive it and take it out of OD. Suspect the tranny fluid needs changed as it's past due. Gonna drop the pan and replace the filter like I always do.

 

trans service huh.......... wonder if that could be my problem......... my fluid is "orangeish" doesnt smell burnt but should be changed.