Still battling a rough Idle issue - Any thoughts?
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Author:  White2000 [ Fri Feb 19, 2016 3:25 am ]
Post subject:  Still battling a rough Idle issue - Any thoughts?

Hello everyone and thanks for looking into my rough idle adventure.


The rough idle appears once the engine is warm (idles inconsistently normal then low). It can be instigated by using electrical accessories such as the fan or the brake pedal. When doing so the rpms (~650-750) and voltage (~13.89 from 14.55) both drop. The vehicle does not stall.

The vehicle drives great. I averaged ~32mpg when i bought the vehicle last year. I currently average ~38mpg.

Here are things I have done in attempt to solve the issue as well as make the vehicle run as efficient as possible.

- Cleaned then replaced IACV
- Cleaned throttle body
- Checked compression (numbers were better than expected)
- Smoke checked for a vacuum leak (no leak)
- Replaced PCV
- Replaced spark plugs (properly gapped)
- Replaced coil lines/boots on the ignition coil packs (spark tests passed)
- Replaced fuel injectors and tested to ensure they received electrical signal
- Back probed then replaced Map Sensor
- Back probed then replaced TPS
- Replaced both 02 Sensors
- Replaced thermostat
- Replaced coolant temp sensor
- Upgraded to 105A alternator/Upgraded Battery (voltage is 14.55 except for when it drops to 13.89 during rough idle surges)
- Replaced + Wiring from Battery to alternator
- Replaced ground wire from battery to transmission and added grounds from engine to body/battery to body
- Removed factory paint at grounding points in the engine bay (wiring harness and head light grounds)
- Replaced Starter wire from battery
- Added a ground wire from transmission to the starter mounting bolt
- Tested the car for parasitic draw (no shorts reported)
- Replaced crankshaft position sensor
- Replaced camshaft position sensor

The vehicle drives great, but the surging/low/rough idle undermines how fantastic of a car this is.

The list above is what I remember doing so far. I apologize if I forgot to mention anything.

Any input is greatly appreciated!

- Mike

Author:  crazyman [ Sat Feb 20, 2016 4:19 am ]
Post subject:  Re: Still battling a rough Idle issue - Any thoughts?

Dirty stuck open EGR valve?

Author:  White2000 [ Sat Feb 20, 2016 7:10 pm ]
Post subject:  Re: Still battling a rough Idle issue - Any thoughts?

I don't believe my car has an EGR valve.

Author:  Stupidmouth [ Sun Oct 23, 2016 4:29 am ]
Post subject:  Re: Still battling a rough Idle issue - Any thoughts?

Have you used Marvel Mystery Oil before? Its an oil additive, but I wouldn't consider it snake oil. I've used it on a couple other older cars w/ different issues and MMO + oil change (or drain a bit and top off w MMO) helped pleasantly.

Same deal using it last week on my first metro (97 LSI 1.3)...pulled great, sounded great while driving but idled rough...up down up down dowwwwwwwwwwwwn. Gave it the trusted MMO treatment in crankcase and gas tank...idles much better now it really does "purer" like a kitten :D ... merReviews

Author:  VladTheImpala [ Tue Nov 22, 2016 1:26 pm ]
Post subject:  Re: Still battling a rough Idle issue - Any thoughts?

OP have you tried the MMO trick? I am having a similar issue and I'm thinking about trying it. I just had an oil change a couple of weeks ago, so I'm going to try draining a bit and topping off with MMO.

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