Hi idle after changing sparks plugs

I would recheck the timing.

(2WD) L4-2559cc 2.6L SOHC (4ZE1) (1991) (2WD) V6-3165cc 3.2L SOHC (6VD1) (1993)
(4WD) V6-3165cc 3.2L SOHC (6VD1) (1993) (4WD) L4-2559cc 2.6L SOHC (4ZE1) (1991)
2WD V6-3.2L (2003) 4WD V6-3.2L (2004)
LS 2WD V6-3.2L (1999) LS 2WD V6-3165cc 3.2L SOHC (6VD1) (1997)
LS 4WD V6-3.2L (1998) LSE 2WD V6-3.2L (1999)
LSE 4WD V6-3.2L (2000) S 2WD L4-2.2L (1999)
S 2WD V6-3.2L (1998) S 2WD L4-2559cc 2.6L SOHC (4ZE1) (1997)
S 4WD V6-3.2L (1999) S 4WD V6-3165cc 3.2L SOHC (6VD1) (1997)
Sport 2WD V6-3.2L (2001) Sport 2WD L4-2.2L (2002)
Sport 4WD V6-3.2L (2002)

follow this link as easier than me trying to talk you through it then bookmark page for future reference
Mitsubishi Montero Spark Plugs

generally they play up under load like going uphill in top gear. Put some load on then try pulling away up hill in top gear, if smooth uptake then they are ok. Or remove and hv tested at auto electrican. cheers

depending on what engine you have, the labor is 1.6 for the 3.0 v6 and 2.2 for the 3.5 v6. assume most shops charge $90 a hour for labor plus tax you're lookig at between 170 and 200 just for labor then plugs from mitsubishi are $13.73 retail, but aftermarket platinum plugs are a lot less, like $8 each. so depending on what plugs between 35 and 85. so unless you are wanting to do it yourself you are looking at between 200-250 for the 3.0 v6 or 230-290 for the 3.5 v6. if you are local i woudl do the job for way less : )

Did you solve this problem? I am having a rough time figuring this one out on my 99 Montero! Maybe the ignition control module (power unit) or an ECU problem? Please let us know if you have solved it! Thanks

If you'll need to remove the intake (or plenum) from the engine there are @ 8-10 No. 12 nuts and or bolts which hold this in place. There are also 1-2 bracket (check by the firewall) you'll need to unbolt too. Be certain to replace the gasket that is found between the plenum and the intake and do not over tighten these nut/bolts only 20ft pounds or so. If you do remove this you'll have to remove the air inlet, throttle cables and remove hoses from the throttle body, some of which carry coolant to properlly preheat the air before enteringthe engine. I have worked on several early 89-93 Monteros without having to remove this for plugs; perhaps different under the hood of the sport.
I hope this may have helped,
Tom

Do one at a time and change the wires while you are at it. Do not over tighten plugs!

If you are sure that you have removed everything that is holding the cover to the head, you may need to use a bit of force to get it off as it may be glued in place. If your plugs go in through the cover, they must be removed .