Engine "miss" at 25-30 mph

[linda7915]

When driving in traffic, pulling away from stop, accelerating on freeway onramp, etc. at about 25-30 mph, the engine misses, sort of like a loping thing, then it runs fine once it gets over 30. It also idles just fine. We took it to the Chev/Workhorse dealer and he put the scanner on it. Found codes P0404 (Exhaust Gas Recirculation Circ Range/Perf), P1514 (Air Flow to TP Sensor Correlation Hi) and P1635 (5 Volt Ref Lo). Unfortunately, he can't figure out the underlying issue and is suggesting a new throttle body, followed by a PCM if that doesn't solve it. He can't say specifically what is wrong and if the $800 throttle body (plus labor) doesn't fix it, it can't be returned. NO! Not a good solution, at least not at this point.

More about symptom: Engine actually only stalled one time. I was driving, thought it was on cruise but had hit the brake and took it off. I was actually coasting along on the freeway and the RPMs just kept going down. When I hit the gas to speed back up, MH had stalled. I pulled over and was able to start the engine right back up. This time the Service Engine Soon light came on steady. This is the only time this light came on and when we got home and turned the engine off, it did not come back on when engine was restarted.

Has anyone experienced this? Know what might be wrong? Do you have a good mechanic in the Orange County CA area who has experience with Chev/Workhorse vehicle? Looking for some input here, anything. Husband is retired auto tech. He understands the codes, but has no experience with this engine and no connections to anyone who has this experience.

Mileage on this MH is about 36,000

[overlander63]

Try unplugging the electrical connector to the egr valve, and drive the motor home. This will turn the MIL on, but it will let you know if the valve is the culprit. If it sticks open it can cause rough running, and the engine will stall at idle.

[ROBERT CROSS]

Originally Posted by overlander63

Try unplugging the electrical connector to the egr valve, and drive the motor home. This will turn the MIL on, but it will let you know if the valve is the culprit. If it sticks open it can cause rough running, and the engine will stall at idle.

^
X2

EGR valve sticking would be the best place to start.
Our 454 Burb went thru the same symptoms after 100k, random stall on deceleration, rough idle.
I can see it happening on a MH that doesn't get used a lot.

Bob

[Punch]

One suggestion: I had a similar problem on a throttle body Ford 460 years ago, seemed to occur when the tank was down to a third or so. Computer scanning by the dealer was unhelpful and the car left the dealership with a hefty bill and the same problem! I eventually found (without the benefit of a scanner) that there was water in the gas tank, and presumably at a lowish level on the tank, a sudden demand for fuel and change in ignition advance led to stumbling and stalling.

Probably not your problem, but worth considering.

[Waipio Rim]

Okay, this is a long shot, but I lived with our old carbureted 310 showing symptoms pretty much like you describe for the first three years I owned it. I finally came to the conclusion that the fuel in the line that comes up the front of the engine from the fuel pump to the carburetor would vaporize when it was moving too slowly, i.e., foot off the gas. That line is also directly behind the radiator, and gets hit with all of the hot air coming out of it. I finally wrapped the line with header wrap and pretty much solved the problem.

You have a fuel injected engine with higher pressure in the lines, giving the fuel a higher boiling point, so this is most likely not your problem. Just in case you might want to look for places where a fuel line comes too close to a hot spot like a header pipe.

[92landyacht]

Yep error code P0404 is EGR and code P1635 can also be related to the EGR harness. Code P1514 can be a wide variety of issues and also can be related to the above.

[linda7915]

Quick update.... we bought a Scanguage II, hooked it up, cleared the codes P1514 and P1635, only these 2, no EGR code), and drove. When engine cold, nothing, runs great. When it warms up, has the "loping" or "stuttering" or "bucking", whatever you want to call it only when it is going between about 10 and 30 mph, and NO CODES come up. Previously, we had a 2nd occurrence of engine stalling. We had pulled over, turned the key off, turned it back and it ran fine (except the slower speed thing), all the way home. This was before we bought Scanguage and we took it by a friend's tuneup shop to look at the codes and he reported it died at 63mph and set the 2 codes then. We ended up taking it to Redlands Truck and RV. That's where it is now. Should know about Tuesday what's happening, hopefully.

[cwf]

Originally Posted by ROBERT CROSS

^ X2 EGR valve sticking would be the best place to start. Our 454 Burb went thru the same symptoms after 100k, random stall on deceleration, rough idle. I can see it happening on a MH that doesn't get used a lot. Bob

+2^^

also, an intermittent "ignition" module or cap/rotor if yours has them.

I had car which the dealer couldn't fix... Replaced the "pickup" inside the distributor that is a "Hall device"... Ran fine for 150k miles.

If carburetor then make sure the choke is opening.

[linda7915]

We think it's fixed! Took it to Redlands Truck and RV. They found that the ignition switch had a burned wire and connector. This is something that Workhorse has experienced before and they even have an updated replacement for it. Redlands RV found some other inconsistencies in the electrical and traced it to this switch. He said he is 99% sure that this is the problem. We drove it back to Irvine from there and did not have any trouble, so we'll see how it goes on the next trip out.
2003 Airstream 30' Land Yacht, Workhorse P32 chassis

[cwf]

Thanks for update! Good catch!