skip or hesitation under power

[yelkenli]

94 Camry
5S FE with AC
168,000 miles (mix of around town and highway)

I am tracking down an issue that is hard to describe, but any of the following might be used: skip, hiccup, lope. I will call it a skip. the issue could also be described as a transmission gear change.

1) the problem seems to occur more when warmed up. especially after highway driving.

2) on the highway, it will occur when the transmission downshifts to climb a hill. about 2 seconds later, there seems to be a second transmission shift. again, this is the feel. it might be described other ways. this uphill climb scenario is consistent.

3) In park, in a parking lot, if I turn on the AC, which adds load, i will get a couple of these skips within a minute of turning on the ac, then it idles OK (idles rough, but characteristic of this engine). if i turn off the ac, i do not get the skips.

but this was only repeatable after highway driving, and I could not repeat after a quick trip around the block. after trip around block, without AC, i had some skips.

4) driving around town, i get these skips periodically. I first thought the transmission was the issue as it seemed to occur with a transmission gear shift.

5) the skips do not occur regularly. at idle for example, it may idle for long periods, and when driving, it may drive for long periods, without problem.

6) when accelerating from a stop, it seems to skip just after pressing on the pedal, somewhat like a hesitation, but more like a transmission gear change. this is not consistent.

RPM speeds (maybe not relevant, but i recorded these when trying to observe the rpm drop due to the skip). after trip around the block:
idle, park, w/out AC - 750
idle, drive, w/out AC - 750
idle, park with AC - 875
idle, drive with AC - 800
when going from drive to park, the idle dips to 700, then recovers to 750.

A moderate skips seem to drop the RPM by 50 to 75 rpm

Maintenance
Fuel filter? i have no record of a filter replacement (I do not have records before 1999 - will ask seller - my dad). I read online that the fuel filters should not require service on a toyota (?).

spark plugs. replaced 17,000 miles ago.
spark plug wires: i have no record of a replacement (I do not have records before 1999)
distributor: replaced 2.5 years ago. two weeks ago, dealer told me i was getting oil in the distributor due to seal leak

air filter - replaced last year.

Timing belt - two weeks ago, dealer replaced timing belt, other belts, oils seals, water pump. This problem pre-dates this timing belt change.

pulled 3 inch air hose from TB. carmelized, but does not look like anything to worry about. I will try some fuel system cleaner via the fuel tank.

Any ideas you might have would be great.

Any recommendations on what to check, please advise. I have moderate skills, no specialized tools.

Thanks,
Ted

[yelkenli]

Another note:
my gas mileage seems low. i have not paid too much attention since most stations only offer gas with ethanol.

[gorckat]

I had similar problems after a plug/wire/cap/rotor change. The new ignition rotor was a little loose on the distributor shaft causing misses that felt exactly like what you describe.

Given the plug/wire service history you have, I think they're all due, and a new cap and rotor wouldn't hurt, either.

ADD: Not sure what you need to do about that distributor seal leak, however. That might be related, or not at all.

[eyeball96]

Do a search on Seafoam, do it! See if that helps.

[yelkenli]

I replaced the spark plug wires last week, and the problem has gone away (I am confident). We have not had any rainy weather, and I recall the problem being worse on the interstate when it was raining. However, this would still point to the wires.

I purchased the Toyota wires from the dealer. The cost was higher, but my thinking was that the wires I replaced lasted maybe 15 years and 150,000 miles before noticable symptoms. The only risk here is "they don't make them like they used to". I will not find out though.

I did look at the recommdations for other wires, but most people using those are replacing them frequently. I will agree if someone argues that my MPG efficiency could have suffered well before this skip problem drove me to action. I have noticed a loss of MPG. I attributed it to the ethanol that is present in all the fuels. But maybe my electrical system was degrading. Also pushing me to go OEM was several forum threads recommending going OEM on anything electrical. The cost difference was minor as well (though percentage-wise, 60% more).

Thanks for the recommendation, and I hope this thread helps others.

Regards,

Ted

[eyeball96]

Glad you got it fixed dude!