420A 1995 Eclipse 420A Rough/Shaky Idle

[Ribalfire]

Hello All,

Recently picked up a 95 eclipse that has a very shaky idle. When revving in neutral it smooths out completely. Trying to figure out what the cause could be. Any assistance or recommendations are appreciated.

I have verified compression in all 4 cylinders, spark on all plugs. Not seeing any vacuum leaks. Possibly injectors?

 

[BLACK'98DSM]

Have you scanned it for codes? Sounds like a misfire.

 

[Ribalfire]

Well, the battery has been dead. Just put a new one in an ran it for a few minutes but it’s not throwing any codes. Not sure how long it would take before it would detect.

 

[Ribalfire]

I found a crack in one of my motor mounts. Could this cause issues?

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[pauleyman]

no. That is not the cause of your shaky idle.

 

[BLACK'98DSM]

Could this cause issues?

no. That is not the cause of your shaky idle.

Well, to answer the OP's question directly: Yes. That could cause issues. But not the issue you're having. Replace the mount before the center of the bushing becomes separated from the rest.

 

[Ribalfire]

no. That is not the cause of your shaky idle.

A bit of an update. Verified timing was 100% correct. Good compression, Replaced IAC, deleted EGR, cleaned throttle body, replaced bad motor mount. Still very shaky. Engine idles very steady at 1k RPM but shakes bad. I attemped to bleed cooling system so I removed radiator cap and started vehicle. Coolant almost immediately started overflowing... possible bad head gasket? Oh and I only have one CEL which is the emissions for my EGR delete. No misfire codes or anything.

 

[pauleyman]

So what were compression numbers? Did you change anything? Plugs? Wires? When you verified timing are you talking ignition timing? Or mechanical timing?
Is this car new to you? Are there any other symptoms? Overheating? Does it drive well? Accelerate well?
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[Ribalfire]

I am getting 175 across all cylinders. I have tested good spark across all wires/plugs although it wouldn't hurt to change them I suppose. Coil pack resistance seem ok. I verified mechanical timing (camshaft and crank marks line up perfectly), I was not aware you could modify ignition timing with the 420a. I have not checked injectors yet. This car is new to me, bought it as a project and do not know much at all about it. I have not driven it long enough to verify if it overheats or not...I am concerned to drive it with how shaky it is at the moment so cannot speak for it's drivability at the moment. I could take it out and see how it does but just didn't want to damage anything. Seems to have a throw-out bearing issue as I hear a rattle when the clutch is not pressed but have not ever had that cause shaking like this.

 

[pauleyman]

I would at least check spark plugs and wires although it would likely show up as a misfire CEL. Basic tune up stuff at least. You said you didn't see any vacuum leaks, did you actually check? Like run a test? I would certainly include that in diagnostics.

 

[Ribalfire]

I have not run a vacuum leak test yet. I suppose that it probably a missed step that needs to be performed. I've actually not done this before. I think my best bet would be to rent something at autozone? Spark plugs look good, they seem very new. I have not checked resistance on my plug wires yet. Not quite sure what I should be reading for those.

Apparently smoke test is the most effective?

 

[Ribalfire]

I would at least check spark plugs and wires although it would likely show up as a misfire CEL. Basic tune up stuff at least. You said you didn't see any vacuum leaks, did you actually check? Like run a test? I would certainly include that in diagnostics.

I bought some carb cleaner and sprayed anything that I could think of that might be vacuum leaking with no luck. I noticed a possible coolant leak from the back of engine... I bought an exhaust coolant leak test kit but I couldn't even properly do it because my coolant bubbles up so quickly and constantly even when it's cold to the touch. I'm thinking either blown head gasket or intake manifold gasket?

 

[BLACK'98DSM]

A bad intake manifold gasket won't cause a coolant push. It would cause a vacuum leak though.
Have you pulled the plugs to see how each cylinder is burning? If the head gasket were bad you would likely see signs on the plugs.

 

[Ribalfire]

I don't see any issues with the plugs but I guess I'm not quite sure what to look for. I've already started tearing it down...going to replace head gasket, water pump and intake manifold gasket. I bought this to learn on so figured I may as well.

 

[DrewmHolland]

Hey I know this is an old forum but I’m in the same boat, my 1999 gs has been freshly rebuilt, 180psi compression across all cylinders and good spark and fuel but for some reason it shakes at idle, I’m guessing it’s because I deleted egr but I would really like it fixed since a rough running engine isn’t a good thing. when I’m on the gas it smooths out beautifully but for whatever reason it hates to idle

 

[BLACK'98DSM]

Deleting the EGR does not cause a rough idle. If anything, it would reduce the likelihood thereof.

What kind of crankshaft pulley are you using? If it's the OE harmonic balancer, check it for damage. I would also watch it rotate at idle to make sure it stays true. If you have an underdrive pulley installed, it is not the cause.

 

[DrewmHolland]

I do have an aluminum 25% underdrive pulley installed, whats odd is it shakes more when i start it cold and smooths out as it warms up, its easily driveable but still far from perfect.

 

[DrewmHolland]

UPDATE: so far it still has the same issue but I pulled the plugs and noticed they’re all perfect, they couldn’t be any better. However… cylinders 2 and 3 are a kind of shiny brass color and cylinders 1 and 4 have a mat black finish, it’s not burning oil and the plugs indicate perfect running conditions. IDK WHATS GOING ON!

 

[DrewmHolland]

Here’s a side by side of pistons 1 and 2

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[DrewmHolland]

Spark plugs couldn’t be better

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[DrewmHolland]

I can promise you there’s zero smoke from the exhaust and I’m not burning coolant

 

[DrewmHolland]

UPDATE: I just checked fuel pressure and it seems like I may have a set of leaky injectors, when I shut the car off fuel pressure dropped from 43psi to 5psi in roughly 30 minutes so im guessing the extra fuel being dumped at idle is causing it to run rough but smooth out once im on the throttle. new injectors are on the way so we'll see where this goes.

 

[Brad Bell]

UPDATE: I just checked fuel pressure and it seems like I may have a set of leaky injectors, when I shut the car off fuel pressure dropped from 43psi to 5psi in roughly 30 minutes so im guessing the extra fuel being dumped at idle is causing it to run rough but smooth out once im on the throttle. new injectors are on the way so we'll see where this goes.

Any more updates to share?

 

[DrewmHolland]

Well it turns out my flywheel bolts came lose and shifted if off center which was causing the shaking and after a painful afternoon of taking off the starter and adjusting the flywheel with a chisel it runs smoother than anything else in the driveway

 

[DrewmHolland]

As for the fuel pressure I think my gauge was on its way out since it crapped out on me later