surging

[steve]

I have a 2005 Aveo (100,000 miles) that has recently begun a low grade type of surging that is primarily only noticable during unaccelerated cruise. It idles great and no surging during acceleration and no check engine light. I replaced the plugs, ran some fuel injector cleaner as well as some new gas. Before I start replacing parts, can anyone give me a steer as to what the potential fix might be?

[avguy]

Can you post what the tach shows while this is happening? Both the RPM fluctuation range, and also the time duration as the the cycle is happening.

[steve]

The tach stays rock solid but the hesitation (probably a better term than surging) occurs about every 25-30 feet when travel at 55 MPH. The very slight hesitation occurs in all gears and like I said is most noticeable during non-accelerated events though a slow acceleration can also cause the hesitation.

[avguy]

Did changing the plugs have any effect at all on what you're noticing? How old were the plugs that you removed, and did they look to have normal wear and condition? How about oil in the plug wells? Oil in the wells is very common in these engines, due to valve cover gasket leak, but lots of oil over time can rot the plug wires.
Have you tried pulling and holding the throttle wire to get a constant high idle, to simulate your "cruise" situation? If you can duplicate the hesitation, you could pin the wire with a vise grip, and then see if moving wires around changes anything.
One other thing that happens on our Aveos is the throttle body gets gunked up. You can clean the TB and see if that makes any difference. Unfortunately, and as always with these things, there are LOTS of other things beyond what I mentioned that could be causing this hesitation.

[steve]

Hey thanks for all the help. The plugs had no effect on the problem although they had not been changed for over 90,000 miles (wear seemed normal for that amount of time). I appreciate the info on the plug wells. There actually was oil in there and I was wondering where it came from.
You suggested moving the wires around. As I’m not greatly mechanically inclined, can you be a little more specific. What wires am I moving around?
On a separate note, I just got a check engine light with the following code: P0300 (random/multiple misfire). Kind of vague but does this help in narrowing down the possible malfunctions?

[avguy]

The P0300 fits right in with the hesitation, and it's no surprise to see that show up. If there was enough oil in the wells, that's a fairly likely candidate for what you're seeing. I think it's definitely worth a shot at installing new plug wires, especially since it sounds like they've never been replaced. But you need to get as much oil as possible out first - a clean rag swabbed around the wells with a screwdriver can get most of it. And just as important is to get the valve cover gasket replaced asap, or else this same thing is likely to happen again within a year or so. If you don't feel comfortable doing a DIY on this, any decent shop can do the job very easily.
Of course, the misfire could be the result of another problem, but the wires are routine maintenance that should be done in any case, so it's best to do that first. Has the plastic thermostat housing been replaced and the timing belt changed? (separate topics having nothing to do with your current problem).

[steve]

Your suggested fixes were spot on. After changing the wires and cleaning the throttle body, she is running like a champ. Replacing the valve cover gasket was a good call. The old one was quite brittle. Thanks again for the help.

[JusteR]

nj steve, thanks for following up