R170 230k loss of revs

[thegaryg]

Hi R170 experts...can I ask for some advice please re my R170 230k (1998)

Background - I've been stuffed by the covid situation financially (as have many, grateful that were ok healthwise, unlike many, so not whining I hope..) but one small ray was my ageing fatherinlaw giving us his SLK as he no longer drives it. Its pretty close to worthless (rust on every panel, Cat D write off after some lowlifes burglers nicked it and dented the door). Anyways...my local garage had a look at it and said its 'the best car youve ever had' mechanically which was initially great news, then reflected on my money pit S4 (gone) and Doblo...So, its worthless but I love it , i want to drive it as much as poss but cant spend any money on it.I can put the roof back up manually in 90 secs now (the hydralics are fine but i think the electrical connections intermittent.) etc but its just developed a new problem which I would love and be v grateful for some advice on how to sort ...

its just started being gutless, eg overtaking, going up hills. It wont rev over c4.5k in neutral and at 4k the exhaust is making a bambambam noise (like an old motorbike) and the car starting rocking slightly (side to side). On the road it'll go higher maybe up to 5k but not enough to kick down. Im thinking spark rather than fuel but might be totally wrong

Please could I ask for any sense of direction advice (in simple english, you can see I'm a bit clueless mechanically although i can take stuff apart and put it together again). Very keen to drive it but dont want to abuse my local garage guy's good nature by hassling him for advice or more freebie work so though id try myself...but where to start..?

Thanks Gary

[DapperDanMan]

First off get the plugs out and take a look, any cracking of ceramic? how old are they?

Second suspect is a coil pack. Do you notice the issue at idle? If so disconnect each pack in turn and see if the idle remains the same or not. If it does remain the same then suspect that coil pack.

Of course, a diagnostic box would be ideal at this point which could tell you what is wrong. Just a standard OBD diagnostic should pick up coil pack issues.

[thegaryg]

Thanks Dan, I’ll let you know progress

[DS129]

I'm not an expert but I believe all Mercs have a rev limiter in neutral so it won't rev beyond 4 -4500
As others have said, get a diagnostic check done, don't throw expensive parts at it by guesswork.

[thegaryg]

Yes - slightly embarrassed ! I found this out after posting. Like several other faults on this car - it seems to have cured itself this morning. My father in law reckons lots of intermittent faults ( roof sometimes goes back up, sometimes doesnt, remote lost contact with car etc and maybe this) all down to old car old electrical contacts. I'm going to try to source the right hardware and software to do diagnostics. Thanks for the responses so far, much appreciated.

[DapperDanMan]

I use an iCarSoft scanner which gives me access to multiple systems on the car such as Airbag, PDC, Gearbox etc. etc.

I just upgraded to a scanner with room for 10 car brands CR v2.0. The original one is an MBII scanner and as you might have guessed is for Mercedes I will be selling it when I get round to listing it.