Runs great at first, then skips

gswest · 03-12-07, 09:34 AM

It runs great at first start up, but as the engine warms up and the idle slows (as it's supposed to), there is a noticeable engins skip. Also the A/c used to automatically raise the idle, but now the idle doesn't change when I turn on the A/C. I've replaced all the ignition stuff: plugs, wires, cap, rotor. So now I'm wondering if I should replace the TPS. Vacuum lines all look good, and valves have been adjusted twice since the problem started. New valve job a couple of months ago started this problem. Timing was set by my local shop and I haven't checked it, but the truck runs down the road fine, just shutters at the stop lights. Has anyone run into this before?

Stumpalama · 03-12-07, 09:59 AM

More info please:
What is your warm idle speed?
does it behave the same in neutral?
are all your plugs firing? are they fouled? gapped correctly?
Check you vacuum switching valves BVSV 1 and 2., on my '81 they are on the thermostat housing.
You should check your top dead center position of the flywheel vs. the no.1 piston.
Check the vacuum advance on your distributor.
set your timing.
One thing you didn't mention was checking the carb. You should give that a once through as well.
Check you mixture.

gswest · 03-12-07, 11:52 AM

I didn't mention, she's a 1988 FJ62 w/ FI. But the warm idle speed is around 800 rpm.s. When I put it in nuetral the idle goes up to between 900 or 1000 rpms. Still a skip present. As far as the vacuum advance, I haven't looked at that area yet. I'll also pull up the fault codes again, I haven't done that since the valve job and the idle problem started.

nicholastheczar · 03-12-07, 06:36 PM

gs -

Sounds kinda like my 88 62. It had been running fine but recently it has gotten rough. Have all new vacuum hoses, cap, rotor, and plug wires ready to install to see if it helps and just installed new plugs and a new pcv valve.

Stumpalama · 03-13-07, 09:29 AM

OK,
Obviously, alot of what I said doesn't apply

I had an FJ62 as well.
You mentioned fault codes; Is you CEL (Check Engine Light) on?
I might recheck your valve adjustment. did you warm up the truck before adjusting them? What exactly did you have "done" to the valves? They might not be working correctly when warmed-up.
Have you checked your coolant for oil or your oil for coolant?
Also, check your tranny to ensure the shifter is in the right position i.e. fully in drive. Also, check your tranny fluid (the tranny valves could be gunked up too)

gswest · 03-13-07, 12:26 PM

I had a very reputable machine shop do the valve job. They tested all the springs, replaced valve guides and replaced half the valves. I removed and then replaced the head w/ all new gaskets. I did the initial valve adjustment cold just to get it running, then I did another valve adjustment when it was warmed up. I messed up the valve cover gasket reinstalling the valve cover the second time, so I had a pretty good oil leak and that made me think the idle problem was related (loss of vacuum). But son of a gun, I replaced the valve cover gasket and it not only still had a miss, it also still leaked oil. I subsequently found the oil leaking from the infamous oil galley plug which I took care of. That being said, it's now leaking from somewhere that I'm afraid is the rear main seal. I can live with that for now, but the idle skip bums me out. Do you know much about the throtle position sensor (TPS)?

gswest · 03-13-07, 04:57 PM

Oh, and no CEL present. But, when I have checked the fault codes before I had a hit on the TPS, but it was TPS or several other things. So, I didn't bother looking further. At that time it was running smooth though.

overhanger · 03-13-07, 05:52 PM

You have an FSM? Follow the trail it gives to check and quit guessing at what the problem could be. Internet magic bullets won't fix it for you - you will fix by your own good efforts. You can do it and will. TPS stuff is very straight forward. Test it per the FSM for basic performance and adjust it per spec then you can forget it being a part of the problem if the problem still exists. Good luck and keep after it.

cruiser88 · 03-13-07, 05:55 PM

Quote:

Originally Posted by gswest

It runs great at first start up, but as the engine warms up and the idle slows (as it's supposed to), there is a noticeable engins skip. Also the A/c used to automatically raise the idle, but now the idle doesn't change when I turn on the A/C. I've replaced all the ignition stuff: plugs, wires, cap, rotor. So now I'm wondering if I should replace the TPS. Vacuum lines all look good, and valves have been adjusted twice since the problem started. New valve job a couple of months ago started this problem. Timing was set by my local shop and I haven't checked it, but the truck runs down the road fine, just shutters at the stop lights. Has anyone run into this before?

sometimes the tps just needs to be cleaned /and adjusted.the spring in the back of the tps is usaully the failure.if you know how to set them i believe this will help

cruiser88 · 03-13-07, 05:57 PM

Quote:

Originally Posted by gswest

Oh, and no CEL present. But, when I have checked the fault codes before I had a hit on the TPS, but it was TPS or several other things. So, I didn't bother looking further. At that time it was running smooth though.

the tps code does not always throw

i had this trouble last year.and when there is a tps code the computer will sometimes automaticlly throw other codes.after changing the tps,all codes went away

Buckwheat · 03-13-07, 06:48 PM

Idle speed/idle ari control valve sounds bad. Used from Spector, mine cost $250, new they were $500. My problem was a continous high idle. The FSM has a test sequence for it.