New issue with my '57

[RICH MUISE]

I'm not sure if this issue is related to the noise issue I've talked about that has not been figured out yet. Neither happens when the car is cold. The new issue has happened 3 or 4 times in the past few months. If I'm on a highway for a while (the shortest time so far is about 30 minutes last Saturday), and I take my foot completely off the gas, I can feel a slight pulsating, surge, what ever you want to call it, when slowing down. Very similar to not pushing in the clutch on a manual tranny when speed is too slow, but not near as severe. Can barely be felt, more of a hearing it happening thing.
My car has the 4R70W auto tranny and an aftermarket trac-loc in the 9". I'm going to take it out this morning and see if I can get it to do it again, and if I can, I'll take it out of overdrive to see if it stops it.
Any ideas? slipping tranny? Since I was recently made aware of the fact my Yukon trac loc has clutches, could it be there?

[RICH MUISE]

Took it out and put 130 miles on it......tried to get it to do the slowing down issue at least 15 times under different situations. Never did it once.....ran perfect. I guess I'm back to deciding whether to do the NSRA show in Pueblo, Co. this weekend or the July 4 show in Santa Fe.

[Ford Blue blood]

Rich, take a look at the IAC motor.  They get sticky and act stupid.  A couple of shots of brake cleaner with it off the engine may "fix" your issue.

[RICH MUISE]

Thanks for the response. IAC motor........my brain's not working apparently. What's that?

[Ford Blue blood]

Idle Air Control, should be just aft of the throttle body or mounted on it.

[RICH MUISE]

OK, now I'm with ya. May be a non-issue. As of this afternoon I have put 650 miles on the car this week. I just got back from an over-nighter to Oklahoma. Never did it once. Thanks for the suggestion, Bill.
and btw, I did take my gas mileage this time and it's higher than I thought at 22. Still those 70. fill-ups hurt!!, even if we are lower than most parts of the country. Oklahoma is at 4.24 for reg, and 4.59 for mid-grade.

[KULTULZ]

OK, now I'm with ya. May be a non-issue. As of this afternoon I have put 650 miles on the car this week. I just got back from an over-nighter to Oklahoma. Never did it once.

Did you service the IAC?

What type PCM is controlling the trans? Can you get into it with a scan tool?

[RICH MUISE]

Been months now since the car has done it. I have not serviced the IAC. The tranny is controlled by the OEM Lincoln computer....unmodified. Not going to worry about it unless it starts happening again. Yes, I can plug in a scanner, but it's OBDI and not going to be modified. The issue could be related to not-ideal shifting performance when in overdrive (hills, etc). I think due to the rear gear ratio not being the same as what was in the donor Lincoln.