I had the ignition coils and spark plugs replaced on my 95 4.0. After that was done, my engine sometimes now tries to die when I put it in gear. The RPMs drop too low and the engine wants to shut off but then the RPMs raise back to normal and all is okay. One time though, the car did shut off. This only seems to happen when the engine is cold.

Could this be related to the new coils or plugs? Or could my mechanic have inadvertently done something to something else while he changed the coils and plugs?

Thank you for your feedback!

 

How's the behavior otherwise - if the engine were warm (either from letting it warm up or if starting it after a short trip to the shop or something) does it not threaten to die when you put it in gear?

 

It doesn't threaten to die when it's warm. It only happens when it's cold and I put it in drive or reverse. After starting it after its warn, it doesn't threaten to die.

 

What was the reason for changing the coils?
Plugs are a service item but not coils.

I had a similar problem many years ago and one spark plug was shorting back to the engine control module.

If you are 100% sure it wasn't like it before then it's either your plugs or coils without stating the obvious.

Did you use the correct plugs ?

Did you use OEM coils ? I doubt it as they are very expensive.

The coil/plug change is a simple job and shouldn't effect anything else as there's nothing leave off.

Is the car running ok at idle? No misfires ?

 

What is your idle set at? I think 800 RPM is the book value.

Thanks,

John
1987 XJ-S V12

 

My idle when cold is 1100 in park and 850 in drive. When it's warm, its 1000 in park and 750 in drive.

The coils were $95 each so I guess they were aftermarket.

Today I determimed it dies when it's cold and I move it from drive to reverse. I'm not sure now if it is only when put in reverse or when put in drive too. But it must be related to the mechanic changing the coils or the plugs because it didn't do it before. I wouldn't think though that the coils or plugs would cause that though.

 

Original coils cost about 95-115 depending where you get them.

If they have "MADE IN JAPAN" written on them they are OEM.

You may have gotten a bad coil out of the box or s bad plug if the problem started happening right after this work

 

I realize I didn't answer all your questions. Sorry.

I had the coils changed because my car has an intermittent miss when cruising on the freeway. It almost feels like a gust of wind hits the front of the car. I researched this forum and concluded the miss was likely the coils. My mechanic agreed. So he changed them and the plugs. He said the coils were originals. Sadly, it didn't solve my engine miss though my mileage has improved by a few miles to the gallon. He's going to change my fuel filter next.

So now I still have my engine miss plus the new problem of it dying when it's cold and put in reverse. Ugh...

I don't know if he used the correct plugs or not. He's a British car specialist so I assume he should have.

The car runs fine at idle.