Mid-Dec 2012 bought truck. Two days later threw code P0305 (5th cylinder misfire). But running smooth, quiet, but getting about 14 mpg city. December 16 took truck to Brakes Plus for full tune-up - plug wires, NGK iridium plugs, fuel filter, pcv valve, 3 belts, valve cover gasket (they said leaking into spark plug boot causing code). $850. Two days later starts throwing code P0421 (warm up catalyst efficienty bank 1 below threshold). Still running smooth, quiet. Not enough time to check mileage. Outside temps 35-50 F. 5th day after tuneup - cold outside about 16 F. Let warm up a few minutes and drove about 5 miles - started running rough in drive, rough idle. Put in neutral, evened out, seemed to be okay. Same thing on way home that day. Next day, about 18 F. Let warm up, backing out of driveway, stopped for traffic, ran rough with foot on brake in reverse. After that, smooth - to and from work (about 8 miles each way). Yesterday about 29 F. Seemed to run okay. Today about 20 F. Let warm up - intermittent rough driving, not quite smooth idle. Not sure where to go from here. First thought is to take it back to shop. Afraid they will say due to new code (don't know why they didn't check all codes while they had it in there). But if due to new code, why did it run smoothly from purchase until few days after tuneup? Arrgghh. By the way, I am a middle-aged woman with NO CLUE. Just don't want to get bamboozled. Also - future work will be done by shop that knows Mitsubishi, so please don't bark at me about where I took it for work. The shop always has done right by my son who takes 92 Blazer and 01 Jeep Sport there for service. Any help on what to do, what to look for, what to ask, what to expect would be greatly appreciated. Thanks.

 

could be a dirty throttle body or a tps also check the iac motor

 

Thanks - what I am seeing, also. Also misposted first time - tuneup was done January 16, not December, so problem started few days after full tune-up. A motorhead friend said shop probably didn't rehook vacuum hoses correctly. So first will take it back to have them check the hoses they reconnected. Will start with the most obvious.

 

keep us updated

 

Update - took the truck back to the shop. They took it right in - no hesitation. They checked and all connections are secure. They did reclean the coil pack - said it was done during tuneup as was dirty (?) at 5th cylinder, but maybe didn't get it all or something broke loose in there from the tuneup. They checked codes - it is throwing 3 - P0305 (5th cylinder misfire), P0421 (1st bank, catalytic converter), and one I didn't know about - P0205 - Injector circuit cylinder 1. I looked it up and it says a) injector failed, b) open or shorted injector circuit, or loose connector, or c) PCM failed. They are not concerned about catalytic converter - not at this time, anyway. They reset the codes, and I will drive it for a few days to see what happens. It ran fine today, of course. But low temp for the day outside was 35 F. I swear it happens most when temp outside is below 20 F. We shall see what we shall see. Thinking if it recurs may try changing coil pack first? All input is, as always, welcome.

 

a dirty connector on the coil or injector will cause the problem the elec connectors should be coated with die-electric grease to stop the corrosion

 

Truck dropped off at the shop after work today. Ran rough most of the week, until this afternoon, when outside temp went over 20 F. They will drive it tomorrow morning after warming up a few minutes. I went into detail about what it is doing. Let's hope they get it figured out. This is a call-back, so no charge. Curious - if they have to check injector, do they have to take the intake manifold cover off again? I couldn't find anything online that speaks to it. If that don't tell you I'm a non-mechanic, nuthin' will, right?

 

well cool ... bummer ... keep us posted..... i thought you were the velvet monkey wrench.....

 

This is what the shop wrote down: "Code P0205 (inj #5 c/ct fault; Code P0421 - cat efficiency (they already knew this because they apparently pulled the codes AFTER it started running rough, AFTER the tuneup). Needs front end work - tires are bald. (No, tires are not bald - they have a few thousand miles left on them - they inferred this was what was making the truck run rough - I advised I need to make sure the truck runs ok before spending the money on new tires). May need oxygen sensor and cat converter replaced for P0421 code. Vehicle was left overnight - INSIDE SHOP (I told them it had to be outside in the cold) - checked vehicle before starting - ect shows good - tps good - vehicle started right up - idled fine - and then test drove with no problems. May need fuel injectors replaced and pcm replaced - checked wiring to injectors - no problem seen." They they asked me what I want to do next. I asked what they want to replace the 5th cylinder fuel injector - $375 ($150 of that labor). They "think" it is probably that or the computer is going bad. I asked why it ran fine before the tuneup and bad after - I got a shoulder shrug. They have apparently washed their hands of it. I told them I will take it to a Mitsubishi shop, and if ANYTHING points back to the tuneup it will come back on them. I am flummoxed, and will take it to a Mitsubishi shop. I paid these guys $800 to break my truck.

 

run some lucas fuel additive tru it a tank or so and see if the injector clears up