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Rough Idle

1K views 14 replies 5 participants last post by  speedy25 
#1 ·
Have a 1993 Corolla DX. Was on a trip and belt broke. Kept driving and water pump stopped and radiator overheated and ruptured. Engine shut off. Towed it in and replaced radiator and belts. Everything ran fine except I get a rough idle that vibrates the dash in park or drive. No problem when driving, performs fine. Sometimes rough idle not as severe. I changed plugs (old ones looked good) and plug wires. No change. Any suggestions? Seems that it is tied in with the radiator and overheated engine.
 
#2 ·
Hi, welcome to the blown-up car club! I think we've all been there!

Strange that radiator was damaged. At this point, I suspect a blown headgasket. Take a look under your oil-filler and see if there's a chocolate milkshake foam?

And then do a compression test to get an idea on internal health of engine.
 
#3 ·
Thanks for your response. From what I gathered was when the belt broke the water pump was not pumping so the water got extremely hot which blew the top seam off the radiator, steam was everywhere. Just as I pulled over I noticed the water temp gage shoot up to max and the car shut off on its own.

As to a blown head gasket and compression check... I had the car towed to a mechanic and he replaced the belts, thermostat and radiator and said the car was "ready". It actually runs fine just the idle was rough. If it was a blown head gasket or compression problem wouldn't the mechanic have repaired it? And wouldn't the car run poorly? It runs fine. In fact I took it on a 800 mile trip recently. Just the idle is the issue. Should I still check the compression and head gasket? Thanks.
 
#5 ·
I checked for any head gasket "leaks" and don't see anything. Haven't checked the compression but I don't notice any decrease in engine performance at all. What I did notice was the vibration (at the wheel) decreases when the car is driven for a few miles so I'm assuming once the engine gets to full operating temperature it helps. However the vibration in the steering wheel is still noticeable and you also get a buzz noise from the dash too at idle and when driving. Under the hood when the engine is running you can't tell anything is wrong except if you look at the window wash fluid reservoir you can see the liquid vibrate. We are not talking about "severe" vibration. I can live with it as it is since it seems after reading other posts people have spent upwards of $1,000 fixing things and it didn't solve the problem. The perplexing part was the vibration began after I picked up the car at the mechanics after he replaced the radiator, thermostat, and belts. I suspect it is tied into that somehow ... could I have damaged the engine due to the extreme heat, like bending a rod or? It's a mystery!
 
#6 ·
I have a few crazy ideas.

Since coolant flows to the Idle Air Control (IAC) valve, maybe that overheated and got damaged. Are you sure it's idling at the correct RPM?

Maybe the new belts are too tight, making the engine work harder at idle. Check how tight they are.

The front motor mount is near the radiator. Coolant got on it and damaged it or the mechanic loosened it and forgot to tighten it. Check that mount and the other mounts. Maybe he loosened the right one. Neither actually needs to be removed or loosened to replace the v-belts or radiator.

You are low on power steering fluid. It actually takes Dexron type ATF in the PS reservoir.
 
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#7 ·
Thanks for the info. The belts are tight but there is a little play in them: Im not sure how tight they are supposed to be though. I checked the power steering fluid; it is full and I don't get any whining when turning so I don't think that is the problem.

I was reading another similar thread and they said use berryman b12 choke and body cleaner. Does this apply to me as the car is fuel injected? The other thread also said to disconnect the battery to reset the computer. Should I try that?

Today the vibration was obvious and remained so even when the engine temp ran at normal temps. The weather today was colder though. You get this buzzing noise from the dash and you can feel the vibration on the wheel. Mind you it isn't extreme but it is noticeable.
 
#8 ·
Forgot to add ... guess I'll eventually take it to a mechanic and I will have him look at the engine mounts and belt tension. I will bring up the IAC valve. I don't have a tach gauge but I feel confident the idle is okay as it doesn't want to stall. The vibration still occurs although to a lesser degree when I step on the gas. It is still noticeable when you are driving on surface streets at 25 mph or so. When on the freeway you don't notice it really.
 
#9 ·
You should get a compression test if you don't find any other reasons for the rough idle. Low compression in one or more cylinders will cause a rough idle, but it will smooth out at higher RPMs because the piston is moving faster so the air doesn't have enough time to leak out before combustion. Seeing that it overheated enough to cause the engine to stop running, it could have caused some internal damage, and a compression test will rule this out.

That front mount is by the lower radiator and you should be able to see it or reach down and get a picture. On that mount it's pretty easy to see if the rubber is detached from the metal.
 
#10 ·
Okay ... I'll check it out ... can't do it right now as I need a compression tester, and I'll take a look at the engine mount. Thanks for your help. If anyone else has any suggestions let me know. If anything I can take the list to a mechanic if I can't figure it out myself as I have limited tools and knowledge.
 
#11 ·
Overheating will cause damage, but not necessarily a blown head gasket. While a compression test many give you some idea of the internal engine parts condition a leakdown test does a much better job AND lets you know what the problem is.

In any case, rough idle is typically from internal leakage. Testing will determine which cylinders and how much.

-SP
 
#12 ·
okay .. just saw instructions for the test and it seems for it to work the cylinder must be at TDC (top dead center). Not sure how to set it up that way ... hoping Auto Zone has that meter to loan out ....

Let's assume there is an internal problem ... would it eventually get worse and will the engine just stop working?
 
#13 ·
TDC on the compression stroke. I use a phillips screwdriver to check for TDC. Be careful it doesnt get stuck at an angle as you raise the piston up. I doubt Autozone has a leakdown tester. Harbor Fright has an inexpensive one but be warned that the gauges SUCK and should be replaced out of the box. Its still cheap after replacing gauges.

-SP
 
#14 ·
okay thanks ... I just may bring it to a mechanic versus buying new gauges.... I'm thinking if the gauge does show an internal engine problem is it worth fixing? The car is old, worth under $1k I'm sure. Auto Zone does have a compression gauge.

When I pulled the old spark plugs they all looked great. If it was an internal engine problem wouldn't the plugs look bad?

If it is an internal engine problem would it get worse? If not then I can probably live with the vibration. Just don't want to be pouring hundreds of bucks in a car that doesn't have too many years left if any.

Any thoughts?
 
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