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2002 ford Ranger 4x4 4.0 with 92,000 miles.  Started missing ONLY when at an idle.  Sometimes it would die.  Decided a tune up was due since it'd never had one.  New plugs and wires, still missing.  New oxygen sensor... still missing.  New coil pack... still missing.  Finally... took out Mass air flow sensor, cleaned and guess what??? it stopped missing.. but now there's a bigger problem, transmission acting up.  

Here's what I know: the only thing wrong with the truck before the tune up was that it would not kick into passing gear no matter how hard you tried, but you could shift it yourself and it would do fine, and it missed at an in gear idle and sometimes even in park.  No noise, no slips and no hard shifts from tranny. Actually even pulls a loaded trailer fine.  The tune up was completed in one day.  We tried each part individually until we got a fix.  As soon as we went through each part and it didn't fix it, we replaced the next one.  After we replaced the parts we had bought, we decided to try the MAF sensor.  We took it off, cleaned it and put it right back on.  As soon as we fired it up and put it in gear, the miss was gone, but it jerked real hard into gear.  So we drove it anyway and it jerks real hard from 1st to 2nd and from drive to OD.  It also jerks or slams into gear from drive to reverse or reverse to drive.  We immediately knew the tranny was bad... and then we began to ponder, 'How does a tranny do fine up until the very moment you start replacing electrical components?' and then we realized it may not be the mechanics of the tranny but instead some electrical component.  Not to mention, IT PULLS A LOADED TRAILER WITH NO PROBLEMS except the hard shifts.

I also have a 2005 ranger identical to this one.  When the 2002 started missing, i decided to do a 0 to 60 test, 1/8 mile test and a 1/4 mile test and time each truck to see the difference.  There was less than 2 tenths of a second difference between the two in each test and we tried them more than once with the same driver and same person keeping time.  We knew then that the miss was not affecting the power, just the idle, so we decided it was a simple problem to fix, and it was. The only difference we could find in the performance of the two was that the 02 would not kick into passing gear, but the 05 would.  Other than that, they were identical.

Since the tune up, the 02 does NOT run any better than it did.  It's no more powerful and still does not kick into passing gear, but the tranny shifts hard. Since the power was the same BEFORE the tune up and the tranny showed NO signs of problems beside passing gear, how in the world did the tune up change it? I don't care to have the tranny rebuilt if it'll fix the problem, but I'm afraid it will not.  In fact, it'd be a heck of a lot easier just to get a rebuild then try to figure out an electrical issue, especially since it is a vehicle in our fleet and money isn't really the issue, it's that we really need the vehicle to drive.  So what do you ppl think? A tune up performed in a matter of about 5 hours proves no power improvement but exposes a bad tranny??? Doesn't sound right to me.

I've read a whole heck of a lot of posts that stated identical shifting problems as mine that were not fixed after more than one tranny rebuild.  No one seems to have an answer to the fix.  Mechanics seem baffled and most ppl say, 'just rebuild the tranny.' And I will if need be, but I believe something else is the culprit.  Can you tell me what it is?
By the way, the OD light does NOT come on unless you turn the OD off. It doesn't flash, blink, wink or anything, and usually they will if the tranny is acting up.


Thanks in advance
a very baffled man  

first off... you need a OBD2 scan tool.... one that has the software for more than just the emission system... the transmission is controlled by the ecm...   and a lot of variables go into the shifting...

including the OD light on the dash.. it is controlled by the ECM.. the switch as i recall tells the ecm that you do or do not want OD ...

i was just talking to a ford tech.. lost his job when the dealer closed and we were looking at a ranger pickup...  the conversation got around to the misfiring ford rangers and explorers...  he told me of one day having an identical mazda version next to a mis firing ford truck...  the mazda ran flawless.   they swapped ecms ..    with the mazda ecm.. the ford ran perfect..   with the ford ecm in the mazda.. it ran poorly..   the ecms have the same connector.. but seem to have a different calibration..

i would think that the best buy on a scanner for domestic GM, ford chrysler  would be the Autel MaxiDiag US703 Diagnostic Scan Tool that is on amazon.com   i have their lessor model from harbor freight and love it..

i do plan on getting one of these..  but i don't do a lot of transmission diagnostics..


there is also a manual position sensor on the side of the trans... the shift lever sticks through it..   it returns various voltage levels to the ecm to tell it what position you have selected..    there have been problems with them on some models...  with a scan tool... you can sometimes look at the voltage return to the ecm..    with a digital volt meter and a wiring diagram..  you can see if it is throwing voltage spikes...

i don't think that all transmission codes will turn on the check engine light..  

i will do a little more research.. there is at least one transmission pro that comes on a few times a week..

keep checking back...  

Always scan the computer before buying any parts.The computer will increase line pressure in the trans to alert you to various electrical problems.Since you had no kickdown im betting on the throttle position sensor.Also the MAF is suspect since its the last thing you messed with.  

It was the throttle position sensor.

Thanks Guys