: Lurching idle



Dadillac
05-24-13, 10:52 AM
For several weeks now my 2008 N* has been idling poorly. For a lack of a better word it is lurching at idle. In gear or park doesn't matter. But it is more pronounced in gear. The rpm doesn't change but it feels like the car wants to start driving on its own. These are brief occurances but frequent. Once I give it throttle all is fine. Since I thought it seemed like a vacuum leak I have already changed the intake plenum, intake manifold gaskets, MAP sensor, also changed the crankshaft position sensor, both knock sensors, camshaft position sensor, wiring harness for these sensors, thorughly cleaned the throttle body and the EGR and the MAF. Next on tap is to change the throttle body gasket. I also bought 4 injectors to swap out a side at a time. This issue still persists and I am wondering if I am missing something. Any help would be appreciated. Thanks
Don

Submariner409
05-24-13, 11:35 AM
Don ........... Long shot, but what about a bad resistance strip in the TPS ? The PCM could be "hunting" for an idle reference.

............ but the "no rpm change" thing is a mystery.

Dadillac
05-24-13, 01:23 PM
Yeah I know right. I think I am going to do the gasket change and injector swap and if I still get nowhere it is time to have the dealer check it out. I just know that it is gonna cost a metric ton to have it fixed there. And that is if they diagnose it right the first time.

Don

Ranger
05-24-13, 10:50 PM
No DTC's?

Dadillac
05-25-13, 04:44 PM
No DTC's. That is what is killing me. This is one time I was praying for a code to set. Anyway I changed the throttle body gasket today. Also cleaned the throttle body AGAIN. Damn they get dirty fast. But no change. I then swapped the four right side (rear) injectors. Although it feels like the issue is resolved I will hold elation until driving the car a few days. Once before I thought it was repaired only to have the issue resurface.

Does anyone know it the injectors has a bench test procedure? Like a resistance check? Or do they need to be on the vehicle to test them? I have a DVD repair manual and the test procedures listed are either on the vehicle or with some fancy test equipment that I do not own. But a simple resistance check I can do. Would be nice to know if one or more injectors are just dirty needing cleaning or faulty

Don

Submariner409
05-25-13, 05:43 PM
I think our injector coil resistance should be 11 - 14 Ohms.

Dadillac
05-25-13, 07:32 PM
I think our injector coil resistance should be 11 - 14 Ohms.

But is that a bench test procedure or an on the car one? The manual I have kind of makes it seem that you use the Tech 2 for that. Just wondering

Don

Submariner409
05-26-13, 11:50 AM
An unplugged injector should measure XX Ω across the two terminals either in the manifold or on the bench.

Dadillac
05-26-13, 08:24 PM
Okay so I changed out the 4 injectors and my problem is 90% cured. Do not want to deal with this anymore so I am buying 4 more. Anyway I tested the 4 old ones. Three of the tested at 11.9-12.3 ohms. The other one went between 11.9 and infinity. Couldn't get it to stay in spec for more than 10 seconds or so. It was bouncing all around. Then I decided to check the other four that I didn't change. Since I had just drove the car the engine was hot. All four tested at about 14.8 or so. I am guessing because of the heat. Also didn't keep the multimeter on there too long because of the heat so I couldn't check for variances over time. Anyway there are 4 more injectors in my future. I will post again once I get them and install them.

Don

Ranger
05-26-13, 09:59 PM
WOW! Injectors are pretty reliable. I'm surprised to hear that.

Dadillac
05-26-13, 10:10 PM
Me too. I would have bet the farm it was a vacuum leak. Injectors didn't even cross my mind. Hoping that changing the other four makes the issue 100% fixed.

Don

Dadillac
06-28-13, 02:07 PM
Ended up being a severe misfire on cylinder 8. And a miniscule misfire on cylinder 1. Dealer installed a good used coil in 8 and the issue is 99% gone. So I bought two coils and when they arrive I will install them in 1 and 8. I will return the used coil to the dealer. But finally it is nice to have a properly functioning Cadillac again

Don

Dadillac
07-02-13, 07:59 PM
Replacing coils 1 and 8 fixed the issue. Engine runs butter smooth again.

Don

maeng9981
07-05-13, 05:10 AM
The individual coils on newer cars die all the time. Beauty covers covering everything and they don't help dissipating heat. Plastic is a lousy thermal conductor. And in most cases they even have those sound deadening material, which also provides a good heat insulation...

I have seen several cars having dead coils within a few years, most of them having individual coils on plug covered by engine beauty covers. Never had any problem with exposed 99 coil packs, or 00 ICM with heat sinks.

ryannel2003
07-05-13, 08:42 PM
Funny you mention that Harry... according to the previous work history on my Deville a few of the coil packs have already been replaced. It was the same situation with my BMW as well.

maeng9981
07-06-13, 02:06 AM
I believe the 04+s have the beauty cover covering the individual coils? The newer GM light duty trucks also have the individual coils and short ignition wires design, but they are exposed to moving air and I have not heard of one dying yet. The ones on trucks will well outlast the plugs and wires.

Here's the L92 that goes into Hummers and Escalades, as well as the top trim light duty trucks: notice the individual coils exposed. 5.3 similar.
http://i.imgur.com/kRVY5F8.jpg

Just to add something, this was Hyundai's solution:
http://i.imgur.com/R7IyXLu.jpg
they made some holes to release heat, but it's ugly in my opinion. Obviously it would be too ugly for a Cadillac. Imagine the Northstar cover with holes.