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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 6899
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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We have a 2003 montero sport with the 3.5 liter engine, it

Customer Question

We have a 2003 montero sport with the 3.5 liter engine, it will start, but not idle well. It hesitates when given fuel, but once rpm's are up it seems ok. When I let off the gas to brake it dies. Local shop said it had a code for a random misfire and needed plugs and wires and valve cover gaskets. I just replaced all those parts and the truck still does the same thing as before.
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.
Hi,
Can you please confirm you have spark from all three coils?
Customer: replied 1 year ago.
Is there a way to do this without removing the upper plenum again?
Expert:  Doug replied 1 year ago.
Absolutely. You can access the plug wires directly on the coils, and unplug them to either install an inline spark tester between each wire and the coil, or you can wear some insulated gloves and hold the wires just off each coil and see if you can see it hear the spark when you drift away.
Customer: replied 1 year ago.
Haven't confirmed spark yet, but the local snap on guy was at the shop this morning and was kind enough to hook his code reader up to the truck. Code is po300 he suggested a bad erg valve. Does this seem possible to you?
Expert:  Doug replied 1 year ago.
Not too likely.
The EGR valves pretty much never fail on these cars....ever. And in the instance that they do you would get an EGR flow related fault. This is because if it is stuck open or stuck closed, the MDP sensor will not see a change when EGR is requested, triggering the fault. And again they rarely fail. The solenoids fail a lot, but then you would be back to either a flow fault or a solenoid circuit fault depending on how it failed.
We need to do this by the book and check things in proper order to avoid buying a bunch of parts you don't need. CHeck the spark at each coil when you can, this is an important first step as it is SUPER common for these to drop control over one coil, and because the coils are on balanced cylinders you will -not- get a cylinder misfire fault, only a random misfire and some rough running at idle.
If we have a problem there, I will give you further instruction on how to narrow down the cause. If we have spark on all three coils then we will proceed with vacuum leak testing and so on.