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350matt, Engineer
Category: Mitsubishi
Satisfied Customers: 21620
Experience:  Mechanical Engineer BEng Hons 22 years experience in car engine industry, 10 years in formula 1
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I've been reading about the rough idle Gallant and I am

Customer Question

Hi Doug I've been reading about the rough idle Gallant and I am having same issue. The car idles fine when in neutral or park but put it in drive under load and the whole car seems like it will vibrate apart. 2.4 2003 Gallant 160k we last week replaced Timing belt, tensioner, adjuster, balance belt, water pump, rear motor mount, transmisdion mount front mount passenger mount, back and front struts, oil&filter change, air filter, transmisdion oil change and filter , alternator, belts, headlights, radiator flush, AC heater blower motor, valve cover gasket. About 6months ago new radiator, plugs, wires, what could be causing this it's frustrating? Help!
Submitted: 10 months ago.
Category: Mitsubishi
Expert:  350matt replied 10 months ago.


does the car pull OK, and otherwise have plenty of power?

Customer: replied 10 months ago.
the car has plenty of power. When sitting at a stop sign or stop light with car in drive and foot on break the car just vibrates so hard and steady it's not a jerky vibration just a strong even vibrant the steering wheel and glove box even the whole dash resonates with a shudder vibration that you can see as well as feel. But light turns green give her the gas and off she goes. I have noticed very rarely when I take off it will hesitate like it might die no sputter or jerk just give it the moderate pedal to start off and it starts off a second later it dies just nose dives for a second and then picks up where it left off but that's rare.
Expert:  350matt replied 10 months ago.


Ok its possibly a slight misfire

replace the spark plugs if any of them fail this checklist:

You can also try spraying some water on the coil pack with the engine running. It is possible the coil is faulty and causing the misfire. If you see sparks arcing with the water, then replace the coil.

I'd check the condition of the injector plugs / connections as this could be a lean misfire if an injector isn't firing properly - the best way to check this is with a 'noid' light

Then check all the connections to the engine sensors one at a time, remove each one and examine for signs of corrosion or damage and a squirt of contact cleaner ( not WD40) will also help.

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and leans the engine out causing rough running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas around each joint in turn. If the engine rev's up you've found your leak.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Customer: replied 10 months ago.
Ok Matt let me give those a try and I will let you know. Thanks for being there.
Expert:  350matt replied 10 months ago.

no problem

just get back to me on this post

Customer: replied 10 months ago.
I definitely will. Thanks!
Customer: replied 10 months ago.
Hi Matt I won't be able to know if your additional diagnostics have helped until my mechanic can get to it this week. I will get back ASAP to you when we are able to work through your recommendations.
Expert:  350matt replied 10 months ago.


Customer: replied 10 months ago.
Hi Matt, I am sorry I haven't rated you yet. The diagnostics you gave me to complete was a little lengthy for me and I have to rent the node testers and fuel pressure kit. I have looked for a vacuum leaks and came across the mass airflow unit that was some air getting by the missing gasket that is like a rectangle with 45 degree corners. Its just missing so I will order one but my brother reminded me that it has been missing for a few years since the mass air flow unit was replaced and the vibration is only a year old. If I rate you before finishing your recommendations and locating and fixing the problem will I be able to come to this question box once finished to either tell you success or in need of next advice diagnostic?