Is my timing off?

[justaguy]

Ok, a few months back I took my '04 Aveo LS Hatch to a mechanic for a new timing belt, water pump and serpentine belt. It was almost immediately after I got the car back that I noticed my idle was a bit rough and the car shuddered a bit when idling. The car drove fine except for the rough idle. I took it back to the mechanic a few weeks later and said my idle has been noticably rougher since the work. He looked at it again and told me I had a bad coil, which he replaced for free. I got it back again and the rough idle and shuddering are still there and just as before, the car drives completely fine except for the rough idle. I went ahead and changed the spark plugs - no difference.

The idle seems to be smoother when the engine is warm. It also seems to be smoother when the battery is disconnected for a long period of time. I haven't seen a strong correlation between the amount of gas in my tank and my idle. Every once in a while the idle is so bad that my RPMs jump a bit, from 800 to about 1200, but this isn't usually the case. Before the timing belt work my car idled around 800 RPM...it still idles around 800, its just rough.

Reading other threads it seems that the usual suspects are the IAT sensor and cracks in the vacuum tubes. Is the IAT sensor the one on the intake closest to the air box? Can anyone provide me the locations of the vacuum tubes? Or should I just assume that my timing belt job was botched? I guess I thought that the car would constantly run like crap if that were the case. Has anyone messed up their timing when changing their belt? How did the car run?


Any help is greatly appreciated.

[y2dgone]

Reading other threads it seems that the usual suspects are the IAT sensor and cracks in the vacuum tubes. Is the IAT sensor the one on the intake closest to the air box?

The IAT is the only sensor on the intake. The other line is to the crank case. Maybe check your PCV

Or should I just assume that my timing belt job was botched?

It's a possibility but you would probably be throwing a code if it was. Your idle controller may be on it's way out

[Wolfman AK907]

Are you burning through a lot of fuel? Also have you filled up since the timing belt change? Maybe a bad batch of water in the fuel. I seem to say that a lot, but you'd be surprised how many service stations get bad gas in their tanks. Try HEET.

[justaguy]

I'll check the PCV valve. I don't believe I've ever replaced it on this car. I seem to remember none of the autoparts stores carrying it. I'll try autozone tonight.

Fuel economy is the same. I've been putting fuel injector cleaners in the tank lately just in case it was dirty injectors...those would take care of water-in-the-fuel issues, wouldn't they?

I'll report back after I replace the PCV.

JustAGuy

[prestoinc]

could be that ethanol ****! it screwed my 99 sierra up... I think it's even what ruined my fuel pump on it. I just bought my aveo and i refuse to run ethanol in it for the life i have the car.. I love my car and i'm not gonna try to F it up with the ethanol like i did my truck.

[justaguy]

Replaced the PCV valve. No luck. I'm pretty confident after further testing that disconnecting the battery for extended periods of time and the level of my gas tank have no correlation to how rough the idle is. It seems to be pretty much random at this point...it's always there, just to varying degrees. Any other advice?

[petrified.rabbit]

this is a long shot with a few questions, but i am relating it directly to the work performed.

it "runs" smoothly but is rough? like shaking? or the rpms are surging?

if it is just shaking, check the passenger side motor mount, i believe it comes off to do the belt. it could be improperly aligned, worn out, or not bolted tight.

if it is surging, and not shaking, i say check air intake sensor, (does the earlier engine have a map or what?) or the throttle body, have you had it scanned or tested? there is a drive by wire throttle body recall i think i heard..

[Monzaveo]

I can tell you this...

I'm not sure if the car would even run like this, but you can EASILY get the timing belt a tooth off.

Here's why...(I was gonna save this for my write up) The cam sprockets move when you take the original belt off. (they wont sit at there alignment mark) and it isnt all that easy to get the belt on perfectly. I used a little trick.

You can tell without to much trouble by removing your airbox, then the top cover.
Not sure of you can peek at the lower timing mark without pulling the lower balancer which may be a bit much if you dont have tools or a garage.

[justaguy]

Replaced the PCV valve - no change.

It turned out to be the timing. I brought it back to the mechanic again and he went all the way back in. Took the belt off, lined everything up, and put it back on. Now my aveo runs really nice again.