2nd Generation Specific 1986-1992 Discussion

rough idle and rattle when starting

Old 10-02-2012, 01:28 PM
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Default rough idle and rattle when starting

So i've had my 87 for about 3.5 years. electrical issues here and there but nothing major. the last issue was resolved by cleaning the main chassis ground and the connections to the main fuse box in the engine bay a couple weeks ago. Car has been running great since... until now...

My brother borrowed my car for 3 days and this morning I noticed it was out on the street instead of in the driveway or the front yard where it normally gets parked so I grabbed my keys and went to move it. Started with a flick of the wrist but EXTREMELY rough idle and with a new noise, rattling akin to shaking a bolt in a coffee can. After about 5 secs the engine died.

Last time I changed the oil my in dash meter was reading a little low, but still about 25 psi at idle and 40ish cruising speed, 2.5-3k rpm. Chalked it up to the lighter oil i put in last change.

From what I understand, the rough idle and dieing could be low compression but then it shouldn't start so easily if that were the case. what has me worried is the loud rattling sound along with the other problems. bearing or apex seal in the housing? any other suggestions or ways to confirm this without pulling the engine? last time I did a comp test, a little over a year ago, i was getting just over 90psi on the front rotor and just at 90 psi on the rear rotor. i'm going to do another one to check for seal failure but wanted to get some input in the meantime.

thanks,
Jason
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Old 10-02-2012, 06:31 PM
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Default Re: rough idle and rattle when starting

i hope that's not it since that's what my car does intermittently. The only issue about it is when this happens my idle wont go to 3k at cold startup, it'll only go to about 1000 which isnt enough for a cold rotary. Turn the idle screw on the intake and see if that helps. I know mine was doing this (the noise is related to rpms being under 500) and it turns out i've got an intake gasket leaking so for the time being (since these cars being what they are auto stores dont carry gaskets) i've got the idle turned up to keep it from stalling when i let off the gas.
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Old 10-03-2012, 11:31 AM
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Default Re: rough idle and rattle when starting

I had to move the car up into the yard so I don't have to try to work on it in the street. Adjusted the idle screw up a little and the car did stay running but still really rough. The tach was bouncing from 1k-1500rpm after the initial 3k warm-up. I was also able to get a better idea of where the rattling is coming from since I was actually able to run around the car while it was on. Sounds like it's coming from the CAT/y-pipe area so time to jack the sucker up and ensure everything there is tight.

I forgot to put this in the original post but the car is an 87 NA with 220k on the original completely stock engine/tranny.
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Old 10-03-2012, 12:26 PM
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Default Re: rough idle and rattle when starting

For the idle conscern. Take the boot off and check the throttle plates and make sure theyre clean. Also theres a idle valve on the opposite side of the intake. Clean it out. Mine was filled with carbon. Cleaning those 2 made a world of difference. Still bounces a little when you do a semi cold start
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Old 10-03-2012, 02:02 PM
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Default Re: rough idle and rattle when starting

tinkered with it a little more, throttle plates look pretty clean. Cat seems tight, as does the heat shield. Waiting to get my compression tester back from a friend now but I started it up for about 30-60 secs and let my dad run around the car listening for the rattling. He's an old redneck mechanic that kept our deputy's cars running for 30 years. He thinks it's coming from the rear rotor... disastrous... with the car idling at 1500 rpm, after i idled it up to get it moved, it sounds like 500 rpm so I'm inclined to agree with him until I can verify compression failure there. the false CAT area I assumed earlier today could have been due to the sound amplifying off the firewall and ground...hopefully I can get the compression test done today or early tomorrow.
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Old 10-03-2012, 02:23 PM
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Default Re: rough idle and rattle when starting

You could also pull a spark plug and listen for the pulses (after removing the EGI fuse, of course), while you're waiting for your compression tester.
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Old 10-03-2012, 02:49 PM
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Default Re: rough idle and rattle when starting

maybe feel for them... I played drums for about 20 years before I learned what ear plugs were xD but just got a call back from my buddy and he's on his way. =D
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Old 10-03-2012, 05:00 PM
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Default Re: rough idle and rattle when starting

dumb came over to help without the only thing he has to help... my friends are great... compression test tomorrow then!
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Old 10-04-2012, 03:01 PM
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Default Re: rough idle and rattle when starting

blown apex seal on rear rotor..... hopefully I can get the engine out of the car and taken apart pretty soon to see what caused the failure and the extent of the damage...
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Old 10-04-2012, 03:52 PM
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Default Re: rough idle and rattle when starting

I think over 220k miles might have had something to do with it, haha.
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