96 850 GLT N/A - Rough idle when transmission engaged

Mark850 · Post by **Mark850** » 14 Oct 2013, 20:13

I have owned this vehicle for about two weeks so I'm just getting familiar with it under the hood. It has been very well maintained and ran perfectly smooth until this morning. After the engine was warm I noticed it would idle rough when I put it in drive or reverse. The rpm's would intermittently drop to around 700 and then kick up again. With the car in park or neutral it runs smooth with no issues. I have disconnected the MAF and that makes no difference. I considered the IAC valve but with no immediate access to replacement hoses I don't want to jump into that on a week night. The hoses all look good going into the IAC.

Time to fess up - I did do some light pressure washing of the engine bay yesterday so I'm assuming that has to have done something. I have checked all the vacuum lines and connectors that I can see and they all appear intact. I removed and cleaned the dist. cap (replacement on order). What concerns me is that the issue is only present when in gear and not neutral. There are no CEL's. Is there something I can check that would directly impact throttle response/rpms when the tranny is engaged?

moacyr · Post by **moacyr** » 22 Nov 2014, 05:15

Same problem here, and it does only happen with hot engine. I had a P0172 code early and managed to fix it. Consumption jumped from 12MPG to around 20MPG. I guess there could be something with the spark plugs or distrubutor.

Also, earlier when on Neutral it would not idle roughly, but a week later even on neutral is rough.

moacyr · Post by **moacyr** » 24 Nov 2014, 06:03

As it follows below

moacyr · Post by **moacyr** » 25 Nov 2014, 05:19

Took every spark plug out to take a look. The electrodes were quite in white colour and the plugs screw were quite oiled.

Cleaned IAC valve.

No change. The problem even got worse with AC on.

Post by **phils94850** » 25 Nov 2014, 07:24

I would start by changing the spark plugs. It sounds like its mis-firing under a load which is common to an ignition issue. Use Bosch copper plugs.

Post by **rspi** » 25 Nov 2014, 07:38

It is likely a MAF issue. If you unplugged the MAF And no change was noticed, I'D say that you have found your pro lem.

Have you scanned for codes?

Post by **erikv11** » 25 Nov 2014, 10:02

@ both people reporting the problem, I agree with Phil you need to first make sure all ignition parts are appropriate for the car, clean and dry and in good condition. Vacuum leaks would be next on the list. Cleaning the IAC is always a good idea if it has been a while but I wouldn't really suspect it here. And yes check the codes if the CEL is on.

@ Mark850: You're right, that test indicates it is not the MAF.

moacyr · Post by **moacyr** » 26 Nov 2014, 03:09

I had a P0172 code, which was giving a rich mixture on bank 1. It was a vacuum leak and I had that fixed.

With MAF unplugged the idle is really unstable.

Yesterday I found an unplugged hose on the canister, which I think it was throwing a P0440.

I took all the wires out to re-tighten the spark plugs. Some codes appeared
P1310 Misfire from at least 1 cylinder - TWC damage
P0303 Cylinder 3 misfire detected

Codes cleaned, waiting for car's feedback

Thanks for your help!
Ps: Already ordered new OEM spark plugs, just waiting to arrive

Edit: Having the P0172 code fixed, it started throwing a slow response from Bank 1 (I don't remember the code number)

Post by **phils94850** » 26 Nov 2014, 06:03

Do you know how old the plug wires are ?

moacyr · Post by **moacyr** » 26 Nov 2014, 12:02

2009 from what I could see on the wire