Weird non vacuum idle cutout issue

Have a question that your not sure what category it fits into or isn't really a specific question about a specific part? Ask it here...
Post Reply
NachtRitter84
n00b
Posts: 7
Joined: Mon Nov 25, 2019 3:27 pm

Weird non vacuum idle cutout issue

Post by NachtRitter84 » Sun Dec 01, 2019 11:17 am

05 sxt atx. 140k Miles. Sometimes starts rough in the cold(advertised when I bought it and fixed with a new pcv valve). Occasionally gets an rpm drop at idle or low speeds, and sometimes that’s enough to cut the engine. I sat outside it with the hood up on idle and there is a faint clicking sound whenever the rpm drop occurs. If it makes a difference there’s also an rpm drop on sharp turn to the left(only), but I recall this being ‘normal’ from the last few atx neons I’ve had over the years. It’s not throwing any codes. It doesn’t have a vacuum leak. The guy I bought it off threw parts at it trying to find the issue, so it’s got new plugs, wires, coilpack, tps, iac. I assume if it was a fuel pump it would throw a code so I’m leaning towards either: fuel filter, idiot threw platinum spark plugs in it(will check on this later) or possibly just didn’t clean it and relearn the idle when replacing the IAC. Possibly the o2 sensor? There is an occasional rich fuel smell during the choppy idle. Any ideas?

occasional demons
Junior Admin
Posts: 19494
Joined: Thu May 03, 2007 12:14 pm
Location: Ashland Ohio

Re: Weird non vacuum idle cutout issue

Post by occasional demons » Sun Dec 01, 2019 5:32 pm

I have run platinum plugs for years and never had one issue.

Bosch, Autolite, NGK, etc. My guess is someone had an issue they couldn't solve and blamed the plugs.

I owned a neon for 3 years before discovering the forums. I put Bosch Platinum plugs in it a month after I purchased it. I ran them for over 40,000 miles, so just saying platinum plugs cause issues doesn't cut it for me.
Bill
dblsg wrote:ya'll a bunch of post whores
Seriously people, this is 2019 not 1920.
2001 Neon ES MTX with '02 R/T PCM
Help support 2GN!

NachtRitter84
n00b
Posts: 7
Joined: Mon Nov 25, 2019 3:27 pm

Re: Weird non vacuum idle cutout issue

Post by NachtRitter84 » Mon Dec 02, 2019 10:46 am

I’ve read a lot of info talking about ‘backspark’ or ‘cross-spark’ from platinum plugs so I’ll still try to avoid them by my personal choice but I appreciate the personal information from you as well, OD. After pulling the iac and cleaning it and relearning it I’m still facing the same problem. I’m thinking it might be the Fuel Pressure Regulator/Filter now? It was mentioned in this post: viewtopic.php?f=67&t=68277
and, like I said, the car isn’t throwing any codes. Just occasional choppy idle to the point of cutting out. MPG seems lower than it should be as well but not by a lot.

occasional demons
Junior Admin
Posts: 19494
Joined: Thu May 03, 2007 12:14 pm
Location: Ashland Ohio

Re: Weird non vacuum idle cutout issue

Post by occasional demons » Mon Dec 02, 2019 11:33 am

The plugs do not create any ‘backspark’ or ‘cross-spark’. The neons use a wasted spark set up, as they use the same coil for 1 and 4 and the same coil for 2 and 3. So both the cylinders are arcing the plugs at the same time. The "wasted" spark is on the exhaust stroke, so there isn't any misfire issues.

People claim that the platinum plugs don't work with a wasted spark design. But I'd like to see the actual research data that backs up those claims. To me, I like something that is a bit more durable, since the plugs are firing twice per combustion cycle. Being I have well over 300,000 miles of use with platinum plugs between my two neons without issue, that's pretty good evidence to the contrary of them being a problem.

They may cause problem under boost, due to not having enough spark gap, but that isn't caused by the platinum in the electrode.


and there is a faint clicking sound whenever the rpm drop occurs.
If the low idle issue occurs when the A/C or defrost is on, it could be related to the load that the compressor places on the engine.

If the compression is low, it will drag the engine down, beyond what the IAC motor can compensate for.

My '01 was so bad at 210,000 that if the A/C kicked on when idling, the PCM shut it off after 1/2 second before the engine stalled. When it first started happening, I suspected a bad A/C compressor, as it would really pull the idle down. Then I did a compression check. at 80 psi per cylinder, it was pretty obvious what the issue was.
Bill
dblsg wrote:ya'll a bunch of post whores
Seriously people, this is 2019 not 1920.
2001 Neon ES MTX with '02 R/T PCM
Help support 2GN!

NachtRitter84
n00b
Posts: 7
Joined: Mon Nov 25, 2019 3:27 pm

Re: Weird non vacuum idle cutout issue

Post by NachtRitter84 » Mon Dec 02, 2019 11:42 am

It being winter I haven’t checked with ac on. Running heat yes, and defrost with that. I can’t say for sure if they are linked. It only happens in idle or in 1st/Reverse coming out of idle. High end is fine. No acceleration issues, no power loss anywhere except at idle or under 5mph.

Poor cylinder compression is... relatively Greek to me, if you’re taking head or valve gaskets i can go ahead and throw new ones at it, the cost is cheap and the job isn’t hard I’ve done it a few times.

Edit: the more mechanically inclines roommate says he has a manual compression tester we can use to test cylinder compression. However, IF the piston rings were bad wouldn’t it make a MUCH louder sound than a faint click which you can only hear with the hood up while standing outside the car? I had a snapped piston on my ‘04 and it was a lot worse than this.
Last edited by NachtRitter84 on Mon Dec 02, 2019 12:11 pm, edited 1 time in total.

occasional demons
Junior Admin
Posts: 19494
Joined: Thu May 03, 2007 12:14 pm
Location: Ashland Ohio

Re: Weird non vacuum idle cutout issue

Post by occasional demons » Mon Dec 02, 2019 12:01 pm

Compression consistently low across the board is the piston rings more often than not. (If it is even low)

The only way to know, if it cranks at an even speed, is by using a compression tester via the spark plug holes.

If it varies the speed while cranking, then it could be rings, valves or a head gasket.

With all the spark plugs out, the throttle propped open, the ASD relay pulled, crew the tester into each spark plug hole, and crank until the gauge stops climbing. Record the number, and move to the next hole.

As bad as the compression is in my '01, the cylinder walls look very nice. The head is in good shape, it was a new head/valves at 175,000. I suspect the rings have just worn enough that they don't hold good tension anymore.
Bill
dblsg wrote:ya'll a bunch of post whores
Seriously people, this is 2019 not 1920.
2001 Neon ES MTX with '02 R/T PCM
Help support 2GN!

NachtRitter84
n00b
Posts: 7
Joined: Mon Nov 25, 2019 3:27 pm

Re: Weird non vacuum idle cutout issue

Post by NachtRitter84 » Mon Dec 02, 2019 10:48 pm

Adding to my headache: the roomie says compression read fine across the board. One thing, and I’ll kick myself in the head if this is it, could it just be a motor mount? I do have a serious low level vibration(we’re taking like a full inch vibration in the rear view mirror) at idle or low speed. With it not throwing any codes, no vacuum leak and compression being fine I’m kind of /headdesk

NachtRitter84
n00b
Posts: 7
Joined: Mon Nov 25, 2019 3:27 pm

Re: Weird non vacuum idle cutout issue

Post by NachtRitter84 » Tue Dec 03, 2019 6:51 pm

Well. I found it. Seems cleared up. Faulty rad cap. Really. New rad cap and reburp on the system and running smooth as glass. The gasket on the old one was.... scary.

Post Reply

Return to “General 2nd Gen Discussion”