hi - new here - I've had my 86 4x4 extra cab pickup since she was brand new - 29 years now- i'm retired, but I used to work about 3 miles from home ,so this truck was driven daily, parked 8 hours and then back home, so consequently it only has 112,00 miles on it - it has always been dependable and ran great until about a year and a half ago - replaced the head gasket, but it has never run the same since - anyway just recently I've been having running issues with it - staggering from stop lights, uneven idle, stalling - I had pulled a code for throttle sensor - so I adjusted that and gave it a good tune - new plugs, wires, dist cap, rotor, filters - still runs bad - yesterday engine light came on and it was really stumbling - got it home, jumped the test plug and turned on ignition but CEL would stay lit solid, odd? - no codes - parked it overnight and this morning no engine light and no codes but it still runs bad - ran some tests - compressions are all good 152-160 - timing is set - but vacuum is way low, like 13-15 at idle - can't find any leaks - seems funny since nothing major happened just driving then she starts stumbling - while the throttle sensor seems to be ok i'm not sure - would that cause symptoms i'm having- any ideas? -thanks

 

Hi there... that truck sounds nice if you only have 11200 miles on it! hehe, but i'm assuming it's a typo and you actually have 112,000 miles right? either way, both are low!

so anyhow, to answer your question, your TPS actually could be the cause. How did you "adjust" your TPS? the question is, did these symptoms happen RIGHT after you started it after the head gasket repair? what was the reason to replace your head gasket? did you replace your chain as well? i have a hard time believing your TPS is the culprit because that's the one thing that doesn't have to be touched when doing the head gasket replacement, unless the wires on the plug got pulled out a little when you had to take it off? so give us more info, although you've given us a lot so far, so good job on that!

 

skebe - the head gasket was leaking about 1.5 years ago - truck still ran ok and it was on my list - I took a trip out of town and while I was gone my wife called and said the truck was smoking and over heating - I don't know how hot it got but I replaced the gasket when i returned - one of the head bolts had pulled and needed to be heli-coiled - after that it just never seemed to run the same - was harder to start, uneven idle, valves sounded diesel-ly no matter what I did to it - don't get me wrong it was running ok ( I drove it a year and a half like that) just didn't seem the same - so maybe it was way overheated when the gasket blew? - chain and tensioner were replaced as was the oil pump - so the current situation has changed since first post - parked it overnight and yesterday started it and it ran great - so now i'm wondering if it's a heat related thing - although I drove it a half hour yesterday a symptoms did not return - or perhaps water related as it's been sloppy here in Denver - so as of right now I don't actually have a problem - strange? - had the windshield replaced three weeks ago - wondering if it wasn't sealed right and water can get down to the ECU - going to check that - and yes it does have 112,000 miles - thanks for answering - oh and I adjusted the TPS according to the factory manual - seemed to adjust ok and is in spec now

 

How the timing on it? When I rebuilt mine I had my timing off one tooth and it ran, it just ran poorly.

 

I did think of that - suppose I could pull valve cover and check - that would explain low vacuum - might be worth a look

 

check for partially restricted exhaust.

 

so if I pull valve cover and set crank at TDC should the mark (hole?) on the cam sprocket be right at the top of it's arc? - as far as restricted exhaust what's a test for that

 

hook up a vacuum gauge somewhere after the throttle plate. rev it to about 2000 rpm. If the vacuum doesn't return to near the same as the idle reading and starts to gradually decrease you have a restricted exhaust.

Example - idle reading @ 20 drops when you rev it up and returns to 18 and then gradually decreases to 15

this is a restricted exhaust situation.

 

on your comment about it being "sloppy," my neighbor was telling me about a vw he had and whenever it was really humid out it would run poorly, even stalling on the highway at times. Anyways, he found out that it was a bad coil or something along those lines that would arc because the plastic had cracked, and you can test this by spraying a light mist of water around the coil, I guess. Not sure if it even pertains to Toyota's, but just a thought

 

junkfan - yea it could have been something along those lines - funny thing it's been nice in Denver since I first posted and the truck has been running great..? - so i'm not sure if I fixed it with the throttle sensor cleaning and adjustment or if it's just waiting for wet weather to leave me stranded - it idles very smooth now but the vacuum is still low - drove it up to boulder today ..ran good but seems like it doesn't have the power to go up some of those hills in 5th anymore - could be age ..something i'm becoming familiar with myself - so right now ..no problems - will check exhaust restriction and leaky wires with spray bottle when I get a chance - thanks for the ideas