Rough idle and backfire/hesitation on cold start

[dc2jz]

Hello ladies and gentlemen,

This is my first post on here. I do a lot of reading but had not registered as I typically can solve problems on my own or find the information needed. I currently have a 2000 C230 sport with 190k that I love, but is falling apart one piece at a time.

I am currently experiencing an issue on my 2000 C230 Sport. Upon cold start, I receive a rough idle with great hesitation and backfiring (possibly knocking as well). If I shut off the car and restart it the problem is gone, and the car runs fine when it registers an increase in temperature on the cluster. I have cleaned and replaced the throttle body, replaced the fuel filter and air filter, checked the spark plugs and coils, and cleaned the MAF. I have another MAF that I will be putting in tonight, but my question is- if I change the MAF and I still have the same problem, what is my next step? I am beginning to think that it may be related to a vacuum leak as one morning when I was gassing it to warm up the car, there was a rather violent backfire that resulted in a loud hissing noise on the passengers side between the air box and motor that disappears when the car warms up. Any ideas or suggestions?

[RemoLexi]

I would never clean a MAF. Your only fooling yourself. Start with a new maf.

[dc2jz]

I would never clean a MAF. Your only fooling yourself. Start with a new maf.

I cleaned my MAF because I didnt want to spend $175 on a brand new one if I didn't have to. Further in my post, I mentioned that I have a new MAF. If the MAF isn't the culprit, where do I go from there?

[RemoLexi]

When your car starts up cold its runs slightly richer, if there's something already causing it to run richer it can be too rich and run poorly. If I had to take a wild guess I've had a similar problem lead to a faulty fuel pressure regulator.

I did not mean to come off totally rude, but too many people seem to believe cleaning the maf is a fix. It's not. They go bad roughly every 70k miles, replace only!

The main objective for the maf is to report to the ME how much air flow is coming through and at what temp, which them the ME regulates fuel mixture. A faulty maf is all too common, I hope that's all it is in your case!

As far as your concern with a vacuum leak, I would assume its not because it would run poor at lower rpm and not at higher (cold startup)

[dc2jz]

When your car starts up cold its runs slightly richer, if there's something already causing it to run richer it can be too rich and run poorly. If I had to take a wild guess I've had a similar problem lead to a faulty fuel pressure regulator.

I did not mean to come off totally rude, but too many people seem to believe cleaning the maf is a fix. It's not. They go bad roughly every 70k miles, replace only!

The main objective for the maf is to report to the ME how much air flow is coming through and at what temp, which them the ME regulates fuel mixture. A faulty maf is all too common, I hope that's all it is in your case!

As far as your concern with a vacuum leak, I would assume its not because it would run poor at lower rpm and not at higher (cold startup)

I was thinking that it was running lean considering how it knocks. There is a very loud vacuum type sound that occurs when its cold, but I havent had the time to take off the air box and look. Tomorrow morning I will know if the MAF is bad since it only runs crummy when cold. After that im cleaning check valves and the egr and inspecting vacuum lines.

[vaspen]

Romeo I cleaned mine 3 times and that's only after a 2 day rain Cus it's moist but mine works fine other than that but yes it may need replaced but 400 for a bosh is steep man ..

[RemoLexi]

I have to dig up the info, but I think there was a $70 sensor-only replacement which didn't include the maf tube.

[vaspen]

8$ quick fix that lasts multiple times to prolong a 400$ fix ya can't really beet untill I spend 400$. In maf cleaner lol

[RemoLexi]

Maf fail for more reasons then just 'getting dusty'. Cleaners leave residual film on the hot film (even though the $8 can says it doesn't) and provide inaccurate information to the ME. You want to rig it that way, sure. But know the function of the MAF and its importance in keeping your cars a/f ratio happy. Especially on a supercharged car.

[dc2jz]

Changing the MAF did the trick. I cleaned the new one just to make sure it was in tip top shape before I put it in. I changed the coils, TB, coolant overflow tank because the nipple had broken off, and all filters in the process of troubleshooting as well as cleaning all of the tubing from end to end. Glad I got everything for free or Id be pissed.

[dc2jz]

Romeo I cleaned mine 3 times and that's only after a 2 day rain Cus it's moist but mine works fine other than that but yes it may need replaced but 400 for a bosh is steep man ..

A few suppliers sell the Bosch MAF for $175ish shipped. They have no name brand ones for $25+ on ebay if you're looking for a bandaid.

[vaspen]

that's why I air gun from afar lightly and yes I know a/f-r is important with me having hot ngk plugs that im going to bosh when I get a chance
but with the ngk and it being this cold out I can feel a disturbance in my cyclender (in a good way haha)

dc2jz thank goodness it wasn't your idle controle valve

[dc2jz]

dc2jz thank goodness it wasn't your idle controle valve

Why?

[vaspen]

whoops my bad I remember vetruck having to replace a 600$ peace or something of the sort in the throttle I forget the name of it at the moment

[dc2jz]

whoops my bad I remember vetruck having to replace a 600$ peace or something of the sort in the throttle I forget the name of it at the moment

I have a few donor cars so i get my parts for free :)

[vaspen]

this guy {~~~ is jelus