TPS/Throttle body swap question (The Saga Continues...)

Topic: TPS/Throttle body swap question (The Saga Continues...) (Read 5095 times) previous topic - next topic

TPS/Throttle body swap question (The Saga Continues...)

April 07, 2005, 01:58:08 PM

Ok guys, I just thought of something. Around last summer I changed out my stock 50mm throttlebody for the mustang 60mm one, but not until today did I think of something that just might be the cause of my "idle rough once after about 3 minutes every start up" problem.

I didn't change out the throttle position sensor. Do I need the mustang one? I mean, appearantly the car will run using the thunderbird one with the larger TB, but will I notice a signifigant difference if I change it out, or was I even supposed to?

Thanks
Matt

Re: Throttle body swap question

Reply #1 – April 07, 2005, 02:06:31 PM

i reused my tbird one. that was with the whole HO tb/egr spacer and intake. i needed to readjust the idle stop screw and the tps a little. it runs fine so based on that i doubt its the problem...

Re: TPS/Throttle body swap question

Reply #2 – April 07, 2005, 02:10:19 PM

Ah, ok. Thanks, I was beginning to think I might have skimmed over a majorly important detail.

Re: TPS/Throttle body swap question

Reply #3 – April 07, 2005, 02:35:39 PM

Quote

A common problem in the EEC-IV controlled 302 Mustangs is a hunting idle. This is an idle which fluctuates in RPM up and down and up and down....It can be very annoying.

There are a lot of tricks people use to try to fix this problem. Most of them don't work.

One common trick (that doesn't work) is to try to "fool" the EEC-IV into thinking the engine is still in warm-up. This is accomplished by installing a low temp thermostat and/or removing the ECT (engine coolant temperature) sensor. It fails when the HEGO sensors detect a too rich fuel mixture, and the EEC-IV compensates by leaning the mixture out. Now you're back to the hunting idle.

The EEC-IV is programmed to idle the car at 672 RPM. Incorrect throttle plate position is ithe primary cause of the problem in most cars. To adjust this, back the screw out until it no longer touches the throttle plate stop. Insert a 0.010 feeler gauge between the screw and the stop and turn the screw until it touches the feeler gauge. Then turn the screw another 1.5 turns. Then adjust the TPS (throttle position sensor) to 0.98V.

Hope that helps ;)

Re: TPS/Throttle body swap question

Reply #4 – April 07, 2005, 07:30:07 PM

Disconnect the idle air bypass electrical plug, turn out the idle screw until it does NOT touch the stop (throttle plate closed), then turn the screw in about 5 turns, start the engine. It will run at a high RPM. Back off the screw until you are reading 675 RPM. Shut off the engine and reconnect the bypass electrical plug. Start the engine, loosen the TPS and check the voltage across the green and black wires with a digital volt meter. Adjust until you read .92-.98 volts. tighten down the TPS screws. Thats it!

Re: TPS/Throttle body swap question

Reply #5 – April 08, 2005, 09:19:05 AM

Thanks for the info guys. I'm gonna mess around with that this weekend.

Re: TPS/Throttle body swap question

Reply #6 – May 02, 2005, 08:40:07 AM

Ok guys I finally got around to messing with it and I think I'm on to something. I didn't get it to quit doing the occasional sputtering/hesitating, but I did get the idle to smooth out to like it used to be. Before I go doing what larrycar78 said, how exactly do I got about adjusting the TPS? The screw on the backside of the throttlebody is the only thing I could know of to adjust.

Re: TPS/Throttle body swap question

Reply #7 – May 02, 2005, 05:24:35 PM

you can take the screw out and elongate the hole allowing for more motion. the tps may be actually hitting your egr spacer and may need to be clearanced. check the idle stop screw also....

Re: TPS/Throttle body swap question

Reply #8 – May 02, 2005, 06:36:19 PM

Not quite sure I follow you about the TPshiznitting the egr spacer. It just has 2 screws that screw right on top of it and I don't see where it can be adjusted...Maybe you have a pic you could show me?

I've been messing around with it, and decided that before I go trying to recalibrate the whole thing by myself, I'd try a few other simple things. I just don't like the idea of disconnecting everything without someone else in the car to kill it just incase...

Well what I did was I noticed it was idling at about 800 when the car was pretty much warmed up. Well I disconnected the idle air bypass and noticed it dropped down to something that sounded much more correct. Well I connected it back and dropped the idle down to about 600-700 ish and it seemed to run fine. Disconnected the IA valve again for the hell of it and it dropped so much it died.

I took it for a test drive and it ran great. Even my transmission problem cleared up. I was able to drive in OD and when decellerating it didn't kick and downshift hard at 30 MPH. Well I pulled into a parking lot, shut it off, and gave it a few, then started it again. It ran ok, but then started the weird shaky hesitation thing again... The OD problem was back too.

I brought it home, checked a few more things and the idle had seemed to had gone back up a bit. Also, I don't know if this is relevant or not, but when I would touch the TPS, and move it just a hair with my thumb, I heard a strange slight electronic ticking/sparking kind of sound coming off of something mounted on the backside of the strut mount area. Weird.

I set it back again about 600-700ish and it still doesn't seem totally right. I figured I'd see what you guys had to say from there.

Thanks again for all of your input.
Matt

Re: TPS/Throttle body swap question

Reply #9 – May 02, 2005, 07:28:54 PM

You adjust it with whatever little bit of play/wiggle is available in mounting it as it is now.. it doesn't take a lot of motion to change the voltage. If you still need a little more play, that's when you mess around with it as has been mentioned here. (widening the holes, etc.) But really, the adjustment is a very small action.

Re: TPS/Throttle body swap question

Reply #10 – May 02, 2005, 07:40:02 PM

Thank you for clearing that up. Well I seemed to have gotten it better...

I just got back in from messing around with it again. I've got the idle to where it sounds like its a hair above 675, just enough to it doesn't sound like its sputtering, smoothed out. I adjusted the TPS turning it clockwise as much as I could (which brought the idle up a bit and it seemed to breathe easier) and then tightened it down. Its not downshifting really wierd at 30 MPH in over drive anymore. How on earth does this have anything to do with the OD problem? Anyways, the idle is still kinda rough here and there, but overall its been a drastic improvement. I'm still not 100% done though. Its still not running like it was a year ago.

Re: TPS/Throttle body swap question

Reply #11 – May 02, 2005, 07:45:48 PM

Hey, no problem. We all have to go through it the first time with the TPS. ("How the @#$! do you adjust this thing when it just has two bolt holes?!") :D I'll be going through it a few more times in the next month or two, as I'm getting this '88 back together and tinkering with the LSC.

Could you live with the idle being just a little bit higher? Maybe try 800 RPM idle with the TPS right at .98v?

I don't know what to say with the OD thing.. I'm still figuring out my three DOAs err AODs. (going a little off-topic here) If I leave it in OD, it'll clunk when I let off the throttle like many of these cars do.. but if I drive around town in D and let off the throttle, no clunk. I've seen from one or two sites that that is a sign OD is not in good shape.

Re: TPS/Throttle body swap question

Reply #12 – May 02, 2005, 07:53:03 PM

I get the same thing with the clunk. Sometimes it does it, sometimes it don't. The whole OD downshifting thing being resolved now has still got my scratching my head...haha. I've been driving around in D for the 8 months or so thinking my OD was out...The overall shifting and everything has totally improved. It used to shift HARD and clunky over 45 miles an hour in OD. Not anymore. All because of turning a sensor about 1/32 clockwise...

I guess I could set the idle back up to about 800. Thats about where it was and I assumed that was the problem, but it seems that the TPS out of adjustment was the problem. I want to go out and monkey around with it again now, I'm sure the nieghbors here at the apartment complex probably think I'm crazy for spending my entire evening out there adjusting the idle! haha

Anyways, as always a million thanks to you guys here at this place. you are always a world of help!

Re: TPS/Throttle body swap question

Reply #13 – May 02, 2005, 09:23:38 PM

Well I'm done for the the day. I really honestly thought I was on to something, but everytime I think I've got it, it throws me for a loop. By process of elimination I narrow down the results to where it seems like I'm on to figuring out exactly whats wrong, but then the variables change. I'm trying to get it down to an exact science to where doing A+B = C, and it works for a few times, and then starts doing something else.

When I adjusted the TPS I noticed it cleared up the OD problem, and got rid of the hesitation problems. BUT it would eventually start after a while and I had to turn off the car, turn it back on and re-adjust. This worked like 2 or 3 times and then all of the sudden even doing that stopped working. The only thing for sure that has come out of this is that the idle has seemed to smooth out somewhat, but not much. I don't really know where to go next. Meh...

Re: TPS/Throttle body swap question

Reply #14 – May 03, 2005, 10:14:41 AM

For the TPS adjustment you need a digital voltmeter. Take 2 straight pins and pierce the insulation on the green and black wires coming off the TPS. connect the leads from the volt meter across the pins and the reading should be .90-.98 volts. tighten down the screws. You can try re-checking the idle adjustment as noted above.