Hello everyone,
I recently bought a 2005 Scenic II K4M 761 automatic. Long story short, my AC compressor suddenly failed while driving, making loud metallic noises. I pulled over immediately as I didn't want to risk the serpentine belt snapping and taking out the timing belt, so I got the car towed to a garage.
There we inspected both belts, and found them in very bad condition, so a new timing belt kit was installed, as well as a new AC compressor and serpentine belt. Note that I didn't notice any prior drivability issues other than a very very slight rough idle when in gear, which I attributed to old plugs and possibly a streched belt. Also, it had a loud dephaser rattle on some cold starts, but that would go away in a second or two, so I didn't make much of it.
Now, firstly, while changing the cam belt, the mechanic couldn't put the locking tool for the cams in because the exhaust camshaft was out of time - We assumed somebody before did the job without the tools and messed the timing up, so we reset it so that the tool would fit, and carried on, hoping no engine damage occured. As I said, the car ran fine, had good power and really no meaningful driveability issues which was mind boggling.
Anyway, everything was changed, the mechanic cleaned the throttle body and opened it fully and then later closed it with his hand (from what I've heard this is a big no-no, but I don't know). So we start the car. The exhaust gases smell horrible, the car won't rev up, it's misfiring, lodging what looks like black oil dropplets out of the exhaust, after finally revving up it smoked brown smoke at high revs etc... So, at this point I'm worried, the car drove fine before, and to me this starts looking like a timing issue. The mechanic changed the spark plugs, and after a bit of revving, the car settled in, and seemed to be ok. I took it for a test drive, it was running absolutely fine when warm, so I said whatever, I'll drive it home and see how it behaves. That was yesterday, I drove it again in the evening for something like 20 miles of city driving, it drove beautifully, so I thought it would be fine.
Fast forward to this morning, I start it up,it started up perfectly, almost no dephaser rattle, so I, quite pleased, engaged D and started to pull away. Well, as soon as I applied throttle, the car started dropping revs, would not accept any throttle (I was pushing the pedal more than 50% of the available travel, but it just wouldn't rev up), and the rev counter started showing 0 (engine was still trying to stay running) then bouncing back, accompanied by what seemed to be hard misfires and an engine on the verge of stalling. So I try to back up, when I put it in N it was better, but as soon as I engaged R and put it under load, the engine could not sustain the idle. Somehow I put it in N and floored it, thats when I managed to rev it to 3k, then it dropped to a bit steadier idle, so I managed to back up just slightly to avoid holding off traffic. After a few minutes, when it warmed up, it would rev up, but there was still a misfire at idle. I managed to drive it back to the garage where further diagnostics will be done in a few days.
Exhaust smelt very bad, as if it was running on paint thinner or something, just a horrible strong smell, when revved up it would leave a black tar-like substance on the pavement, and the idle was unstable, but it was driveable when warmed up.
I'm now wondering a few things:
1. Could a faulty dephaser cause these symptoms via messing up the valve timing so bad that it would cause incomplete combustion? Makes me wonder was the exhaust camshaft purposefully out of time to compensate for the bad pulley, if the pulley is able to mess things up so bad?
2. Could the throttle body cause this after being manually opened and closed? Does it need calibration?
3. Has anyone else had something like this happen on their Renault before? It almost feels like an extremely rich running issue, but haven't yet done any diagnostics myself
I don't want to chase my tale with this one, I'd rule out anything not related to the previously done job (such as coils, sensors...) for now as it seems unlikely that a separate issue occured right after the belt change.
Luckly, I work at the garage that did the job as an advisor, so I can monitor and determine what is going to be done next. I think that, after diagnostics, a compression test might be my best step forward, just to rule out engine damage.
All of your comments and opinions are welcome. Thank you.