2.5 intermittent miss at idle

Sunk · Aug 22, 2010

Well I've been kicking myself for not buying a code reader I saw at a garage a while back for $20, and now I'm really kicking myself. It seems there's some BS law that means a $10,000 fine for loaning a code reader here in CA.

So I ordered one for $40, and it'll be here sometime this week. I didn't want to right now, but it'll be well worth it in the long run.

bigjim240z · Aug 27, 2010

Ok, here is what i found on my po302 code, if you look up my post on what i changed (all for nothing) you will see i tried all the common problems. Took it to a friend who has been a chevy mechanic for the dealership for 30 plus years. He checked everything i did and we came up with our best guess that has helped the problem. Its not ignition, fuel or emissions related. Its an oil pump issue. Yes, read it again, an oil pump issue!! Ok, let me explain before you tell me I'm an idiot. The oil pump has a check valve or relief valve in it to relieve some of the oil pressure. With the hydraulic lifters if there is too much oil pressure it can keep a valve open. So if the check valve in the oil pump isnt working correctly (stuck or plugged) it will have high oil pressure and keep the valve open just a little causing the miss. We put in 5w 20 oil with sea foam in the oil and bam, it runs 100% better and 2 weeks now with no po302 code. I wanna pull and change out the oil pump but its 212.00!!! Thats one expensive pump. Im thinking about pulling it and trying to take it apart to see what's going on.

Sunk · Aug 27, 2010

That's interesting... Keep me updated post back up if anything changes. My code reader should show up in the next couple days so I'll be able to tell what's going again. If it's just high oil pressure like that, I wouldn't be too worried about it.

The guy I bought it from said it's done for a while and it's been reliable otherwise the whole time.

Sunk · Aug 27, 2010

Well my tester came in the mail today, so I plugged it in and got a P0455 EVAP Control System Large Leak (0.080") Detected. I see some people have fixed this with with a new gas cap or filler neck. Looks like the fuel fuel neck is quite pricey though.

Sunk · Aug 27, 2010

I checked out the truck a little bit; with the engine running I can't smell gas around the tank or under the hood. I can unplug the canister vent solenoid and I get no change.. I'm not sure if that means anything though.

So a leaking or stuck open CVS generates a P0455 from some of the research I've done. It can also be caused by Vapor Management Valve (purge solenoid) that is stuck closed.

http://www.motorcraftservice.com/vdirs/diagnostics/pdf/obdsm307.pdf

The truck has about 1/4 tank of gas in it. The gas cap is the screw in kind that only turns about 1/8 turn before it clicks and is locked.

Sunk · Aug 30, 2010

Well I crawled around underneath it a bit, and the EVAP lines look okay. I decided to pull off the fuel filler neck since it didn't look that great. I got it apart and there was quite a bit of dirt and surface rust around where the metal pipe meets the rubber hose. So I sanded that clean until both pipes were pretty smooth. I got it back in and it seems a bit better. At first the idle was very smooth but It seemed to come back after the truck warmed up a little bit more.

I plugged the scanner back in to see if there were any pending codes since my CEL was not on, and I got P0301 and P0443. P0443 is for EVAP Purge Valve Circuit Fail, so I'm betting I caused that by unplugging it before. P0301 is Misfire on Cylinder 1, which I had a while ago.

I'm gonna clear the codes and see what happens if anything. I should have checked for codes before I did anything, but I didn't think about it.

Sunk · Sep 2, 2010

I filled up yesterday and put about 80 miles on it. It seems like it runs better with a full tank, but it's hard to tell since it doesn't do it all the time. I crawled under there a bit today and looked/felt around and it looks like a small amount of gas leaked from the top of the tank and down the side. I'm not sure it from the fill or vent hose or around the sender. I'd pull the bed off and find out, but I have a lumber rack and canopy on and nobody to help lift it off. Plus I don't think the landlord would appreciate that.

Sunk · Sep 12, 2010

Well I thought it over, figured out a way to prop one side of the bed up and mess with the tank last Monday and was all set to do it Tuesday when I was offered a job. So that didn't get done, but I put about 300 miles on it and 5+ hours of drive time and no CEL or pending codes. I'm not sure how long it should take or if it varies, but I'll post up it I get something. I changed the fuel filter this morning too and as fas I can tell, no change. I wasn't expecting any, I just thought I'd do it.

Sunk · Sep 23, 2010

The CEL FINALLY came back this morning on the way to work again, P0455 again. When I first fire it up in the morning or after it's sat for a little while it cycles between rough and smooth idle. I can hear a solenoid or relay clicking under the hood in time with the cycling, so I'd imagine it's the EVAP solenoid, but I don't know if that's the problem or if it's trying to compensate... I'll try to mess with it this weekend.

Sunk · Sep 30, 2010

I pulled the bed off last night with some help... I pulled all the hoses off the top of the tank and inspected them, they looked ok. I pulled the lock ring off the sending unit and there was some dirt in there, so I wiped it clean as best I could and made sure it was tighter when i put it back on as it wasn't that tight to begin with. The hoses to the canister by the spare tire look ok too. I put it back together and no change...

I hate throwing parts at it, but it's tempting.... :annoyed:

Sunk · Jun 15, 2013

Well I thought I should update my own ancient thread now that I finally found the solution after nearly 3 years and 40k. I've been through and either tested or replaced pretty much every sensor, wire or plug possible and still couldn't find anything. I checked over and over again for vacuum leaks, swapped coils, had a couple injectors cleaned (separate problem) and I still couldn't find anything. I did some more looking around online and found a number of people will the same symptoms that determined they had a recessed valve seat or seats, so I decided to pull my head. I was getting a Misfire Cylinder 1 code almost every time I started the truck so I was fairly sure what I would find.

#1 is on the right. The exhaust valve was visibly recessed and I measured it at around 0.040".

I took it to the machine shop, and right away they noticed what seemed like a crack between the intake and exhaust valve seats on #1. They did a magnaflux anyway and confirmed the crack. Since it would have probably been $500 to get that head fixed I went ahead and ordered a rebuilt head off eBay for $329 shipped. I threw it back together yesterday, and it's like a whole new truck now. I'll have to get used to not rocking my foot back and forth between the brake and gas at stoplights to keep it running. All in time to roll over 200,000 miles on the way home..

Insanejughead · Jun 16, 2013

I started reading this thread, and about three posts up, I realized that it was from 2010...

Silly me. At least you figured out the problem. It'll be good for people to realize that some issues are somewhat minor, but can be caused by a crack in the head around the valves.

Sunk · Jun 16, 2013

That's why I revived it. I spent a ton of time searching online and I found tons people with similar issues, but most of them were able to resolve with a new IAC valve, or it turned to be a vacuum leak, etc. I also saw a lot of questions left unanswered, and that's always frustrating.

Insanejughead · Jun 16, 2013

I've tried to do a lot of going back through certain threads and explaining things so that those searching in the future can get a more solid idea on what will help.

I REALLY want to go through and eliminate all the times that noobs post up that you have to buy a new head because of how a broken timing belt on a Lima motor breaks valves and pistons...

Which reminds me... I need to make my instructional video on how to replace a timing belt on these motors, and then post the youtube link on TRS.

2.5 intermittent miss at idle

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

Sponsored Ad

Sponsored Ad

Member & Vendor Upgrades

Truck of The Month

Recently Featured

Follow TRS On Instagram

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store

Sponsored Ad

Sponsored Ad

Sponsored Ad

Amazon Deals