New Plugs and Wires - Rough Idle

[Marccus]

After installing new plugs and wires, the engine is running "rough" at idle about three months after the fix. In fact it started right after I let the car sit unstarted for three weeks while I was back east visiting. For two months prior to that (after installing the new wires/plugs) the idle was smooth.

As soon as I started it up for the first time after returning, I had to keep feathering the throttle to prevent it from stalling for about 5-10 minutes . After that, it started fine and settled into the throttle setting I has always seen on the tach, but it kept running "rough".

No acceleration or driving problems.

There are no codes and I also installed a new air bypass solenoid and air bypass valve when I installed the new plugs and wires as the solenoid was defective.

The idle will sometimes also "chug". I've always had a smooth running idle and never felt any vibrations in the seat before.

Any ideas?



'89 SHO w/ 356,000 mi.

 

[shospeed]

it might ba a ground issue check allthe ground cable on the intake and by the passanger side hood strut.

 

[sdpatt]

What brand of wires did you use? That is about as long as some cheap wires lasted for me before I learned that the Motorcraft wires were worth it.

 

[masho95]

What brand of wires did you use? That is about as long as some cheap wires lasted for me before I learned that the Motorcraft wires were worth it.

Along the same lines, what plugs were used?

 

[Marccus]

I used Motorcraft wires as I always have. The Motorcrat double platinum plugs were no longer available so I used the Motorcraft plugs that are sold by FordPartsNetwork, etc., for the SHO.

The idle seems a little better, but it still isn't as smooth as it used to be.

Upon initial start in the morning after sitting overnight, the idle is rougher and sometimes when I let the clutch out to go forward from a stop, there is a loss of power for a second or two - a hesitiation - and I don't move forward that much, then I surge forward. Kind of like almost a stall with no power then a surge. Feels like a delayed reaction as the throttle is opened rather than instantaneous.

After this initial happening, everything is fine, and just the idle remains a little rought.

 

[mylaw]

Have you checked the timing !

 

[sdpatt]

Have you checked the timing !

The electronic engine control (EEC) does that many times a second. The only way to alter the ignition timing on the SHO is to add an EPROM chip to the EEC, re-flash the internal EPROM or alter the fixed, 10 degress BTDC mounting of the crankshaft position sensor.

 

[DemonNeno]

From what i remember, yanking the power to the IAC ( the cylinder shaped part near the TB, beside the runners) should choke the motor off. If it doesn't, try cleaning it. I don't know what ended up being your situation, but i'm dealing with this problem right now. It's been a month, have you figured your problem out yet? I have IDENTICAL symptoms.

My car was wandering for idle at first. 1K rev to 1,500, back to 1k, up to 2k, down to 1,500 and would start this process all over again. Changed the TPS, now this problem is gone, but the car idles ~650-900RPMs... hmmm.. Haven't scanned the codes yet, been too busy. We'll see what happens.

 

[Marccus]

I had a vacuum leak which caused the fuel/gas mixture to run lean.

The oxygen sensors couldn't switch between lean and rich as they do when the computer is properly controlling the fuel input based on the mass air flow which is varied by the throttle.

So the computer switches to rich operation (continuous lean operation is bad since it can lead to temperatures) when this problem arises and hence the "rough idle". See my the other post ("KOEO .... " by me in which rangerj tells me to look for a vacuum leak when I had the rough idle problem. The guy is a genius.

 

[DemonNeno]

Thanks dude! Just before i read this post, i decided to check the intake. After removing it, i found all the rubber attached to the runners and the crossover tube are cracking on the OTHER side of the intake (bottom side). THAT'LL cause a idle problem, eh?!

FYI - there's a post by "Miethos" discussing a possible kits and what to be aware of. SHObros is on the job, thank GOD!

http://www.shoforum.com/showthread.php?t=66000

 

[Black '93]

Did you smear any dielectric grease on the ignition where the wires connect and on the plug end of the wire?