engine hesitation

[mercurygm88]

I also notice a hesitation when slowly opening the throttle from a stop, but if I depress the accelerator more than I normally would there is no hesitation. What do you all think about my TPS not reading .98V-.99V and reading 1.2ishV?

This I have this same problem as well I guess it may be possible that both of our problems are simply the TPS I havent replaced mine yet but I do know that it is not the original one. Also I have mine set at exactly .93 volts, did you try adjusting it by moving the tps or using the stop screw on the throttle plate? I was able to set mine by wiggling the tps before I knew that you were actually supposed to use the screw. BTW ive been living with this for about 3 months or so and its starting to get very aggravating.

[MattDoscher]

Initially I tried adjusting my old TPS. I took a voltage reading from the green wire on the TPS connector and got 1.4V. After attempting to enlarge the mounting holes on the TPS and eventually cracking one of the holes, I was only able to achieve 1.2V. I bought a new TPS from Ford and still have a high Voltage reading. I am not able to adjust my current TPS to .98-.99 volts. I heard on another forum that I should not touch the idle speed screw. Is this wrong? SHould I try and adjust the idle speed screw? I can see how that would change the position of the throttle plate thereby lowering my voltage reading for the TPS. But would the ECU learn the reduced idle speed if I turn that screw?

[mercurygm88]

Initially I tried adjusting my old TPS. I took a voltage reading from the green wire on the TPS connector and got 1.4V. After attempting to enlarge the mounting holes on the TPS and eventually cracking one of the holes, I was only able to achieve 1.2V. I bought a new TPS from Ford and still have a high Voltage reading. I am not able to adjust my current TPS to .98-.99 volts. I heard on another forum that I should not touch the idle speed screw. Is this wrong? SHould I try and adjust the idle speed screw? I can see how that would change the position of the throttle plate thereby lowering my voltage reading for the TPS. But would the ECU learn the reduced idle speed if I turn that screw?

I was told to do it by adjusting that screw because the way I understand all that screw does is set a stop for the throttle plate therefore adjusting your tps I would double check with someone more knowledgeable but the way I understand it thats what you do.

[MattDoscher]

Thanks mercurygm88. I will try adjusting the throttle plate screw to see if I get a lower voltage reading on my TPS. I will also try unplugging the EGR regulator and testing that too.

[GM_Guy]

The jerking/hesitation is most noticeable while maintaining speed anywhere btwn 35 to 45 MPH.

Drive it in D and see what happens. The steady state 35-45mph range is the OD-D shuffle the AOD does around those speeds since it mechanically determines wether to go into OD and when to drop out of OD, hence the jerking if you are driving around those speeds. Just slip it into OD if you're going to be on the highway.

As for TPS, I'm going to odd man out again and say this magic .99v threshold is a waste of time on a stock lopo. Why? The computer learns what the tps reading is at idle, and it learns what the tps reading is at WOT and bases its response accordingly.

Alex.

[gadget73]

You're not supposed to adjust the screw. that said, if someone in the past has messed with it, the voltage will be a little high. Normally it comes out in the 0.9-1.0 range, but not always. As long as you don't get codes about the TPS being out of range, its fine though. 1.2 should be OK, but I think 1.4 is out of range. It zeros itself like Alex said, though it does have a range that it considers normal. Outside of that range it will assume the sensor is at fault and just ignore it.

One way to maybe determine if someone has jacked with the screw is to try unplugging the IAC. The idle should drop a fair bit, or cause the engine to stall. If the idle remains high, the screw may have been screwed with. Target idle on these is 650-700 rpm, and with no IAC its generally around 500 rpm. Its somewhat common for people to see that screw and crank it in when the car has some sort of idle related problem in an attempt to fix it.

[mercurygm88]

Well i checked timing today and its dead on at 10* and i replaced the tps just for the heck of it so we will see what happens now. Ive got a 25 mile drive in about 2 hours so i will know then. Also it seems i was wrong about the idle screw just what i had read somewhere. Theres alot of conflicting ideas on alot of this stuff my car will die almost immediately after the iac is unplugged and ive never touched that screw.

[MattDoscher]

Thanks Alex. I will try driving it around like you said. If the hesitation is still there in OD and not there in D what would cause this? Thanks gadget73, what you are explaining makes sense in that the throttle stop screw shouldn't be messed with. I will try unplugging the IAC too. Mercurygm88, how did your drive go tonight? Do you still have problems?

[GM_Guy]

Since the AOD has no external input, its only point of reference to shift in or out of OD is the speed your going, and the load that is on it. The speed range that the AOD typically pops into overdrive happens to be between 35 and 45 mph. If you live in Canada, that just happens to be the speed on a lot of our roads, so we get to experience alot of the OD shuffle. Anyway, if there are any slight grade changes, any slight throttle changes, the aod senses this (ie: tv pressure) and reacts according to that. Unfortuantely, the AOD can't see into the future and know that you are only on a very slightly undulating road, following somebody, which doesn't need a gear change in the grand scheme of things, but becuase you are at that special speed, it keeps trying to shift into a gear for the NOW, not the OVERALL, so it ends up doing the OD-D shuffle, and depending on the road that can become a very erratic experience.

If this is your first AOD, or you come from a general motors background, the AOD wants lots of throttle input to do something. This can appear to be a hesitation, if your feather footing it. If you come from a GM background, this is an even more pronounced effect. You will get used to it. Eventually.

Alex.

[miamibob]

I've had Fords my entire life and when I first bought my '87 GM I thought the trany was defective. Still have it and still have to explain to passengers we WILL get to where we are going and NO the car is NOT breaking down!!

[mercurygm88]

Thanks Alex. I will try driving it around like you said. If the hesitation is still there in OD and not there in D what would cause this? Thanks gadget73, what you are explaining makes sense in that the throttle stop screw shouldn't be messed with. I will try unplugging the IAC too. Mercurygm88, how did your drive go tonight? Do you still have problems?

still got a pretty bad miss at 65 or faster. Getting a new TFI module thursday if that doesnt work gonna swap the distributor. Ive changed everything on the thing except the pickup coil so I figure that may be the issue or its the TFI. I replaced the original TFI with a cheapy aftermarket one and got my local autoparts store to order me a motorcraft one today so ill pick up thursday and see how things go. If I replace the TFI and the dizzy and its still there I guess ill have to give up but this didnt start happening till about 2-2.5 months ago. Also this is my first AOD car is well and you will eventually get used to the AOD shuffle at 35-45 as I have. Though you may have trouble convincing your friends of whats going on I have several friends who have never owned a vehicle older than 05 and dont seem to realize there was a time when not everything was computer controlled. I can actually think of 3 of them who swear that shuffle is my trans about to explode.

[MattDoscher]

mercurygm88; sorry to hear you still have the miss going on. Have you tried what gadget73 recommended by unplugging your EGR regulator and tried unplugging your IAC? What did you find out by doing this? Have you tried driving in D and not OD at speed yet? Just curious if you have tried these things and what you found out. I have yet to try these recommendations because the car is w/ my mom in SC and I live in VA, but I am looking forward to doing it to see what I discover. Alex; I'm still not convinced that it's the D/OD shuffle. Not to say your wrong or anything it just seems to me that my AOD shifts fine. It shifts into OD right at 40MPH under normal acceleration and 50-55MPH under harder acceleration. Upshifts and downshifts seem to be fine. Like I said in my first post the car sits alot and doesn't get driven unless I'm home visiting in SC. It seems to me this problem I have is engine related, specifically fuel delivery or emissions. Could be carbon build-up or some stale gas deposits. I keep STA-BIL in it to try and keep the gas fresh when I'm not there to drive it. The sputtering/hesitation will only occur under light throttle to maintain speed either before the OD shift or once in OD at 45-50MPH. If I give it slightly more throttle it goes away, the AOD does not try to downshift into D when doing this unless you apply more throttle pressure say to pass another driver. Then it will downshift into D.

Matt

[mercurygm88]

EGR solenoid and IAC are both brand new it doesnt change a thing if plug the egr vac line, and the engine dies as soon as u unplug the IAC so thats all working correctly. Definately ignition related at this point.

[MattDoscher]

ok, just wondering. I will be interested in hearing how replacing your TFI module went and if it fixed the problem.

[mercurygm88]

Ill definately be keeping every1 updated I really hope its just the tfi and not the dizzy. Not that i cant afford the dizzy just i can think of better things to spend the money on.