Engine Missing with high idle
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Laughing Gas
Joined: Sep 2012
Posts: 880
Likes: 13
From: Northcentral Wisconsin
Engine Missing with high idle
When my EX is idling it idles at a little over 1000 rpms and then revs up to anywhere between 1500 and 2000. And then idles back to 1000 and continues this cycle. Usually it idles below 1000 rpms. There a miss at cruising speed and sometimes at idle. It did it a week or two ago, filled up with gas and went to put it on the scanner and of course it ran fine. Thought it was maybe a fuel issue so I put a bunch of the Chevron injector cleaner in the tank and went through a tank of gas so far. It ran good up until this week and now it is back to doing the same thing. Took it to a mechanic who suggested we try new plugs and fuel filter. He said there are tiny cracks on the tops of the COPS but he doesn't think this is the problem, they are just weather checked. On the way to the shop it ran fine again but when the mechanic took it for a ride he said he could feel a miss at cruising speed but was not doing the weird stuff at idle. Because it isn't happening right now he is having a hard time diagnosing the problem. Any ideas on what is going on?
Elder User
Joined: Aug 2014
Posts: 560
Likes: 4
From: Anchorage, Alaska
Weird revving usually indicates an air leak... Try getting a vac gauge and hook to the break booster, find out what the steady vac is... If the vac there is steady at say 25 or whatever it is on your truck, it means your mechanically sound and its something else. If the vac at the brake booster is not steady then it means you may have a stuck valve or something else going on mechanically....
If vacuum is good and steady then you can start to diagnose by either unplugging a COP one at a time and see if the misfire goes away or get yourself a decent scanner that reads Mode 6. You can then look for misfire codes to determine what cylinder is causing the issue.
After reading about all the misfire conditions on these V10's I would highly suggest going to scantool.net and purchasing a ELM scan tool.
I just purchased myself this as it comes with OBDWiz, which supports mode 06 reading.
ScanTool.net LLC - ElmScan 5 Compact -- ELM327 based scan tool - ScanTool.net
I have a misfire that I will be resolving this Saturday and this tool is going to be worth its weight in gold.
If vacuum is good and steady then you can start to diagnose by either unplugging a COP one at a time and see if the misfire goes away or get yourself a decent scanner that reads Mode 6. You can then look for misfire codes to determine what cylinder is causing the issue.
After reading about all the misfire conditions on these V10's I would highly suggest going to scantool.net and purchasing a ELM scan tool.
I just purchased myself this as it comes with OBDWiz, which supports mode 06 reading.
ScanTool.net LLC - ElmScan 5 Compact -- ELM327 based scan tool - ScanTool.net
I have a misfire that I will be resolving this Saturday and this tool is going to be worth its weight in gold.
Elder User
Joined: Aug 2014
Posts: 560
Likes: 4
From: Anchorage, Alaska
I will be replacing plugs, fuel filter, pcv valve, air filter, any ignition coils that are bad and then running BG 44k through the intake and fuel system. We will then be using his SnapOn tool to verify no more cylinder misfire counts are appearing after. If we get enough time I am going to replace some door actuators as well.
Thread Starter
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Laughing Gas
Joined: Sep 2012
Posts: 880
Likes: 13
From: Northcentral Wisconsin
An update..I replaced the spark plugs and it ran good at the shop. Got it home and it did the same thing this morning only not quite as bad. It was 7 degrees this morning, I did have the block heater plugged in. When starting it idles at about 1300 rpms for a little bit, then surges to 1500, comes back down to 1300, does a little hiccup like it wants to shut off and then it idles down to below 1000 where it usually idles. It didn't seem to be missing at cruising speed but it seems hard to tell with the V10. When it first started doing this I put it on a scanner and couldn't see any cylinders misfiring but it was running great by the time I got down to the shop. I have replaced the fuel filter and plugs but will need to check when I did the air filter and pcv valve. Pretty sure it has all been done within the last 2 years. I am considering replacing all the COPS but it is a pricey project if it doesn't fix the problem.
Thread Starter
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Laughing Gas
Joined: Sep 2012
Posts: 880
Likes: 13
From: Northcentral Wisconsin
We did find a vacuum leak. We'll check the rest of the vacuum hoses later. We put a IAC on recently. I'll try cleaning the throttle body also. It's been running pretty good so I don't want to mess with it until we get our car fixed. The rack and pinion took a poop on the car, so we were waiting for parts. We'll get back to the V10 next week as long as it keeps running good.
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