Solved! 1995 E320 idle shuttering shaking hickup burping problem fixed!

[racing_maven]

Hey guys,

I recently bought a 1995 E320 wagon that would randomly shutter on and off while in idle. It was like a hiccup and it would come and go. However, I could reproduce the problem without fail by idling in gear with the A/C on. It's a common problem and I've had my fair share of surfing the forums for a fix. Good news is that I fixed the problem.

For the benefit of everyone else, here's the chronological progression of what I did and what happened.

Changed Spark plugs => Didn't fix it (previous owner)
Changed Ignition Coils => Didn't fix it (previous owner)
Cleaned the Throttle Body => Didn't fix it (It was REALLY dirty and now the car accelerates smoother)
Changed Wiring Harness => Didn't fix it (But I had to do this anyway since the wires were in such a poor condition that I didn't feel comfortable driving the car. When I opened up the ignition wires, the insulation simply disintegrated in my hands and was shorting)

THE FIX: Changed spark plug wires.

After changing the spark plug wires, I've noticed a much smoother drive and more power. The old ones were the original () and there was obvious corrosion of the connectors that contact the spark plugs. This explains everything. The corrosion increased the resistance of the wires which prevented the plugs from getting their required voltage to light all the gas/air mixture and so the engine would occasionally misfire (shutter). This especially happened when under moderate load (A/C on and in gear). This also explains the increase in power after installing the new spark plug wires. The plugs are now getting their required voltage and so it's able to burn more of the gas compared to before, which gives more power.

Again, I know that I should have done it in increasing cost, but the wiring harness had to be changed anyway. It was a known problem with the car when I bought it, so I already priced that in to my decision.

So I hope this helps others out there who may be experiencing something similar. If you have any questions, I'll try to entertain them.

[Sergio]

Congrats on the fix. Too often spark plug wires are overlooked. I replaced mine at about 190K; old ones were in good shape but since I was replacing the plugs, I figured I replace the wires too.
How did you clean the throttle body? Please explain as this is useful info.
Thanks

[augapfel]

Good info and thanks.
I recently replaced the ignition cables on my 88 TE#2. This car has 205k miles and the ignition cables were the original ones!
I noticed their condition when I did my first stem to stern inspection after buying the car in February of this year and planned on replacing them soon but other events (disasters) got in the way. The worst one onmy car was the cap-to-coil cable that was cracked, blistered, and super stiff in the area where it is clipped to the cap shield.
When the impala 89 300E showed up in the local U-Pull-It a couple of weeks ago I couldn't help notice that the ignition cables looked fresh. Yep, Beru brand with a 2004 date code. For the price (distributor cap, rotor,and cables = $10) I *had* to take them.

[racing_maven]

Originally Posted by Sergio

Congrats on the fix. Too often spark plug wires are overlooked. I replaced mine at about 190K; old ones were in good shape but since I was replacing the plugs, I figured I replace the wires too.
How did you clean the throttle body? Please explain as this is useful info.
Thanks

I'm glad that people are finding this useful. I cleaned the throttle body with throttle body cleaner (I know ) that I picked up from an auto store for $5.

The procedure: 1. Remove the overhead manifold that goes over the engine (the same one you need to get off to remove the engine cover).
2. Remove the black box sitting on the intake manifold. There are 4 hex screws, two are exposed and the other two can be uncovered by removing the rubber caps on top of them. Once you get the screws off, you just need to pull gently (it takes quite some force).
3. Remove the cylindrical rubber extender that goes from the throttle body to the overhead manifold. It was tricky getting to the screw of the crimper. And then even after that, it was still hard to get off. The trick was to put your hand inside and push against the walls to try to loosen it.
4. Remove the 4 hex screws on the throttle body and take it off. Be careful when removing the throttle body since there is a spring, a lever, and a few other connectors that are attached directly to it.
5. With the throttle body off, just take out your can of cleaner and spray it and wipe it off with a clean cloth.

It's about a 2 hour job. This is definitely DIY for a person with medium technical experience.

Hope this helps. I'm eventually going to post (with pictures) my experiences to help others who may be in need to DIY help.

[racing_maven]

FYI: I Just added a guide with pictures on how to clean the throttle body.

[Sergio]

Originally Posted by racing_maven

FYI: I Just added a guide with pictures on how to clean the throttle body.

Thanks! I saw the post with pictures. Very helpful.
How was the condition of the throttle body wiring harness?

[racing_maven]

Originally Posted by Sergio

Thanks! I saw the post with pictures. Very helpful.
How was the condition of the throttle body wiring harness?

It still had some flexibility and I don't recall hearing any cracking.

[jgajito]

You're doing a great job in documentation and troubleshooting!!!
Keep it up and keep us informed.

[racing_maven]

Originally Posted by jgajito

You're doing a great job in documentation and troubleshooting!!!
Keep it up and keep us informed.

I'm just trying to do my part in giving back to this large MB community. I wouldn't have learned so much without it.

[MiguelXJ]

And you are doing and EXCELLENT part man...

I've just recently experienced the misfire under moderate load, havent noticed anything wrong when driving normally... just at idle and under load.

I'm alreay digging ebay for some spark plug wires.

Thanks for the troubleshooting report and keep it up!