Slight engine shudder when coming to a stop

[davidoff]

Hey All,

Figured I'd see if this rang any bells before I started troubleshooting too hard.

I've got a 2000 SR5 that's generally in great shape. Recently I have noticed that when coming to a stop, just before stopping, there's a little engine shudder. I think I'm seeing the tach drop slightly when this happens, but I'm not sure that's consistent. It happens even if I have been off the gas for quite a while, and seems to only happen if the stop is somewhat aggressive. If I'm just casually rolling to a stop, no problem, but if I have to be on the brakes somewhat aggressively over a short distance, it happens. It's minor but it's definitely there.

I recently replaced the MAF sensor so I don't think it's that. PCV valve, fuel filter, plugs, and wires were replaced when I did the 90k maintenance (at ~200k) after buying it about 3 years ago. The air filter looks to be in good shape. I thought maybe it was the TPS but that this happens even if I've been off the gas a long while, and I'm having no other throttle related issues, seems to rule that out or at least decrease the likelihood. Though, I haven't checked it. A quick visual inspection of vacuum lines didn't turn anything up, but a closer inspection there is probably warranted, especially since this only seems to happen when I'm braking.

Anyone encountered this before or have other ideas? Primarily trying to avoid letting something that's starting to go bad, get worse.

Thanks.
Andy

 

[spartacus]

Hey All,

Figured I'd see if this rang any bells before I started troubleshooting too


Have you tried coasting to a stop in neutral and had the shudder occur. if it happens with no load on the motor and you are braking then the rotor warp could be an issue Does the shudder also happen at idle after coming to a stop if so then it could be the motor mounts. if you are coming to a stop and press the brake gingerly and it happens then It could be a pin hole in brake booster or the pcv valve tube could be brittle or have a leak. If all these pan out you can hook up a obd scan tool and see the fuel readings when the tach drops showing a lean or rich conditions then you'll have to determine the cause of lean condition or rich which is a whole other matzo ball.

 

[davidoff]

Thanks for the reply.

This is definitely not warped rotors, but I did have the same thought at first. It's slight enough a shudder than it totally could be something other than the engine's stumbling causing it, but at this point I feel pretty confident it's the engine.

I haven't tried in neutral, that's a good idea. I will try that.That could be interesting.

The only time it happens when accelerating is when I have _almost_ come to a stop, then get back on the gas before fully stopping. And when that happens, it feels like the motor has dropped into the rpm range where this occurs (~600-800rpm) and that it was just going to happen whether I got back on the gas or not. Lots of gut feeling going on in there, though.

I think I'm going to focus on the vacuum lines first, really give them a good once over, and replace any that seem like they could use it, even if I don't see any obvious leaks. Hopefully I don't have to diagnose a rich/lean condition, but if I do, maybe be ultragauge will be helpful. But maybe not, I'm not sure it's fast enough, and without the ability to record, it could be hard to see what's going on.

Thanks for the suggestions.

Andy

 

[WeAreSLO]

I think you may be feeling the well documented phenomenon known as Rear End Clunk. Annoying once you notice it but nothing to be concerned with from what I've read.

 

[curryT4R]

Check the throttle body and see if there is a bunch of black carbon build up. Use some throttle body cleaner and a clean rag and get it as clean as possible. This will probably increase your RPMs but you can disconnect the battery for a few minutes and it should reset everything, but it should help with your concern.

 

[davidoff]

WeAreSlo: Thanks for the suggestion, but I am pretty sure I know what you're talking about (it gets better for a while after lubricating the drivetrain, specifically the sliding yoke), and this is something different. Definite from the front of the truck.

curryT4R: Thanks for the tip. I can't recall it looking nasty in there last I had the intake off, but I'll check again this weekend. Can't hurt.

 

[davidoff]

I found a few vacuum lines that were split at the ends and replaced them, but they were all very low pressure lines and I doubt they were a problem. It was good to fix them regardless.

I also cleaned my throttle body and IACV. Neither was particularly dirty, but the IACV did have some gunk on it in a spot that I could imagine would cause the action to be slow opening from full close or closing the last bit from open. So far I think the issue is gone, but it's hard to say for certain because it's worst when it's hot out, and of course the weekend I do this the temperature plunges. So we'll see...but if things stay good for the next while, I'd guess it was the IACV.

Andy

 

[gamefreakgc]

I found a few vacuum lines that were split at the ends and replaced them, but they were all very low pressure lines and I doubt they were a problem. It was good to fix them regardless.

I also cleaned my throttle body and IACV. Neither was particularly dirty, but the IACV did have some gunk on it in a spot that I could imagine would cause the action to be slow opening from full close or closing the last bit from open. So far I think the issue is gone, but it's hard to say for certain because it's worst when it's hot out, and of course the weekend I do this the temperature plunges. So we'll see...but if things stay good for the next while, I'd guess it was the IACV.

Andy

Actually, my suggestion was to check for a vacuum leak. But looks like you got that handled.

 

[phattyduck]

Could it be the 2-1 downshift? Try getting up to ~10mph in first (leave auto shifter in '1') and see if it does it slowing down from there.

The driveshaft clunk would happen once the truck comes to a complete stop and settles back, shortening the rear driveshaft. In that case, it needs to be cleaned/re-lubed...

-Charlie