As of Saturday 12/29/12, I have a new to me 1999 Trooper LS 3.5L with 184k! (viewtopic.php?f=1&t=66974
Being my logic is already off-kilter by an overmastering desire to purchase the truck, I could use some help with getting back to 100% Isuzu performance. The owner informed me of two issues:
1) RPMs surge up and down or stumble/misfire on occasion, more often when cruising above 50 mph
2) Burns oil, something like 1 quart in 600 miles
On way home from purchase, check engine light came and pulled code P0125 “insufficient coolant temp for closed loop control” which the Auto Zone employee said meant a bad thermostat. Cleared the code and so far hasn't came back after 200 miles I have been able to put on it (didn't touch the t-stat yet).
Twice on coming to a stop the engine has died, but starts up and goes no problem after. When driving, I do notice the surging after the engine warms up and mostly only on the highway. Video here:
In Drive @ 60 http://www.youtube.com/watch?v=8k6-tVtCqsc
In 3rd @ 60 http://www.youtube.com/watch?v=kOBX-CYbkWg
With New Years off, I ran through some simple things today but the issue remains during my test drive tonight. Here is what I did:
*New tank of gas with Lucas injector cleaner
*Seafoam treatment (1/6 in gas, 1/6 sucked up through PCV intake, ½ in crank drove for 30 miles prior to oil change, 1/6 in spark plug holes 3 hour soak)
*oil change 5-w30 high milage Valvoline
*Cleaned each coil pack spark plug/boot end with carb cleaner and applied dielectric grease (some looked a bit dirty)
Also, I noticed cylinder #5 (rearmost passenger side) spark plug threads seemed oily compares to the others, but the tip seemed grey/whitish same as the others.
I will try the following in this order unless there are better ideas:
*Fuel filter (couldn't hurt!)
*Get used coil and swap one at a time to see if is a failing/weak coil causing misfire and possibly surging if computer is trying to compensate.
*Thermostat - if failing with opening/closing, could possibly cause RPM surge I suppose.
*ERG valve/porting cleaning
*Get injectors rebuilt in case one is tired/failing
*Differentials & TOD oil change
*Change A/T oil and filter (not flushed, just drained and filled)
Send me on the right direction with your powers if I am off course!
Reported recent maintenance by original owner (was a 1 owner truck!):
*starter (8/18/11 178359)
*valve guide kit; air plenum, intake & head gaskets; timing belt, water pump, coolant flush (12/14/11 179250)
*Oil/filter change; compression check #1-192 #2-192 #3-190 #4-193 #5-189 #6-189 (12/14/12)
*IAC idel air control sensor (1/30/12)
*engine coolant temp sensor (2/2/12 181179)
*crank position sensor; oil change (2/10/12)
*crankshaft position sensor; clean mass airflow filter (2/13/12)
*cam position sensor; air plenum & intake gaskets; fuel pressure reading pre start 42psi, running 35psi (2/28/12 181700)
Once I get it going, I'll get some pics posted. Is super clean Performance Gold package setup!