dang - joined the hesitation club too!

[bean]

I was pulling a trailer with my "new" 1990 Legacy AWD sedan (auto) and it had a nasty tendancy to hunt for gears and downshift while on cruise.

I thought the car was having trouble with the trailer - but it really wasn't that much of a load - but fearing the worst I just tried to make it to my destination by trying different techniques. What worked best was running at 4000 rpm in 3rd - car was flawless and I had no issues for the next 2.5 hrs. (Headgaskets definitely fixed!)

I stopped over and double checked tranny fluid and spark plugs - replaced the plugs with Platinum NGK's, and added Lucas Auto tranny conditioner.

Ran it the last 1.5 hours at the same 4000 rpm / 3rd gear and it was perfect.

On the return trip without the trailer the car did the same damn thing!

Holding a constant speed the car seems to have a bog or hesitation and drops speed with the same pedal pressure. Feathering the throttle a little gets it back with what feels like the torque converter unlocking. Too much throttle and the tranny downshifts out of OD.

When you use cruise control - it does the same thing - but the cruise just accelerates to regain speed downshifting every 40 seconds or so to maintain speed.

Symptoms passed after a while - but I know that it'll return.

I'm thinking the TPS is acting up or the duty solenoid B (others?) is acting up. Injectors maybe?

Any other ideas I can check?

(I searched the archives and found no mention of constant throttle hesitation / bogging problems...)

FYI:

Current outstanding issues: Purge solenoid acting up (intermittent CEL), Duty solenoid C is acting up once in a while, and the ABS needs the wheel sensors replaced on the right rear.

I have the duty solenoid C ordered with the gaskets, I want to put in a resistor for the purge solenoid, and I have a used sensor for the ABS.

Only other think I need to do is get a new O2 sensor since the car gets pretty crappy mileage.

[THAWA]

Platinum plugs don't sound too good. And you don't have Overdrive. You have 4 individual gears.

[free5ty1e]

the 4-speed autos don't have overdrive as the 4th gear? I thought that's pretty much how all auto trannys did their thing, locking different gears to get different ratios... 1st, 2nd, 1:1 drive, overdrive. Then again I'm not an automatic guy. (just read up on their operation on howstuffworks.com)

I second the objection to platinum plugs. Get some NGK coppers, could only help.

[bean]

I realized that the Bosch platinums sucked - but I've had really good luck with running platinums on my Subie's.

I even used them on the Rally car I was a crew chief on (1992 Legacy Turbo Sedan) Never had one issue with them in competition - so I'm pretty happy to use them in my NA car. (Ideally I'd love to find silver plugs for these cars - they'd be my number one choice for a performance plug.)

Never had a lick of problems with the NGK G-power plugs and I'm pretty skeptical that they would be the problem. They have perfect color to them and the engine sounds fantastic at full chat with no misses or any unusual running problems under heavy load.

The only bad part is this stumble / hesitation / bog on the highway at a constant throttle position.

As for the tranny - I thought for sure that D was an overdrive since it's not ticking over at high RPM at all on the highway. (By overdrive I only mean the ratio is higher that the 1:1 of a direct drive - so maybe 0.85:1 or something like that.) I'll check the book - but I'm pretty sure it's an overdrive...

[azn2nr]

spark wires if you havent already

[bean]

I ruled out the wires... (Pretty sure anyway!)

They feel very soft and pliable like newish ones would be, there's no stray leakage with the engine running, and they test fine with an OHM meter on them twisting them around like crazy to see if I can get some fluctuations - nada...

Could it be the coil pack?

I'm thinking of trying the grounding mod to see if that alleviates it some...

Any other ideas?