I have 97 x300 3.2 and it runs fine when cold, but as soon as the engine warms up it runs rough and very rich. I have changed the coil packs and spark plugs, new air filter and cleaned the throttle body and butterfly to ensure it all runs free with no sticking. All to no avail, any ideas on what to try next?
Oxygen sensors.
Not sure if you have two or four.
Thanks,worth a try, I will try and track them down and have a look and if necessary replace.
Been suggested that the problem could be with the engine control Unit - if I do change it, does the ignition key need to be reprogrammed?
Runs fine when cold seems to indicate that the car is fine in closed loop. Once it starts reading sensors for fueling, things go awry.
Try the oxygen sensors first. They are sensors that do need to be replaced after so many miles. Yours are probably original to the car.
The ignition control unit (whatever that is) is not something that would change when the car is warm or cold.
AFAIR no the locking etc. is down to the security module.
It helps to know where you are located as there are many regional variations!
Check:
My best guess is the temperature sensor. There are two. The first feeds the instrument panel and the second tells the ecu what temp the car is at. It’s this one that is probably faulty. It will be telling the car that is is still cold so keep the choke on, hence the rough running.
Changed both to be on the safe side and trouble persists, going to try cleaning the maf, as a obd scanner showed that the flow didn’t change no matter what the throttle setting. If that doesn’t work will try to fit the two new oxygen sensors I managed to get. Looks a tricky job though they are quite hard to get to.
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I’d stay with the MAF until you can get it to change with throttle.
Two suggestions:
- Clean it using MAF spray. Sounds like you’re already on that.
- Twist (and clean) the prongs on the MAF ever so slightly, so that the harness makes better contact? Some people have reported that the female harness sometimes loses good contact with those male terminals.
Cleaned it thoroughly and it seems to have made things slightly worse! One thing I have noticed is it doesn’t seem to make any difference if you unplug the maf while the engine is running- it sound exactly the same if it’s connected or not. I would have expected some sort of change.
You should have an OBD2 reader that you can plug in and pull readings from the car? If not, it’s time.
It’s not expensive. You can purchase an ELM27 wireless dongle? WIFI only if you have an iPhone, Bluetooth if you use Android.
Avoid the cheap and nasty rubbish ELM27 stuff on eBay. They’re mostly junk.
Go for something like Carista (app and dongle) or, going upmarket, iCarSoft (an all-in-one unit).
Why do you say that?
All of my cheap <$20 ELM27 dongles still work. I’ve been using them for years, troublefree. I am unaware of anyone on these forums having issues with them.
They’re perfect to leave in each car, and since you always have your phone on you, you never have to worry about it getting stolen, or broken. I would hate to leave the iCarSoft device in the car (because you never know when the Check Engine Light pops up). Having one of those at home could be helpful for a deeper dive, or to read and reset the ABS and Transmission codes, but a cheap ELM27 paired to a smartphone is cheap and easy.
I’m not even sure why you would suggest Carista, $4-$10/month? That’s just plain silly. I use OBD Fusion for my iPhone (again, with the WiFi ELM27 dongle, no bluetooth for iPhone) and you buy it once and it’s yours forever. Not sure how much I’ve paid for it, but its undoubtedly significantly less than a Carista subscription. Androoid users rave over Torque, which is not available for iPhone, although there are several apps that use it as part of their app name, but I believe it is not the same.
Took everybody’s advice and bought a Veepeak OBD dongle and downloaded a elm27 software on to my iPad. Works on the car perfectly. The MAF seems to be fine now I a tweaked the contacts as suggested. The problem persists though. I did notice that although the oxygen sensor voltage varies- the trim stays at 0%. This is on both sensors. If you do an emissions reading, all pass except the oxygen sensors, both fail. Am I right in thinking this is most likely what is causing the problem? Many thanks to everyone for their help, much appreciated.
@Veekay, I wasn’t aware that Carista had a subscription model. I paid £59 outright for the dongle and app.
cheap ELM27 dongles
When the 3rd one I had bought - all different brands - died, I bit the bullet.
There is long term fuel trim (LTFT) and short term (STFT). Which one stays at zero? If it’s the long, that’s good.
Are both LTFT the same?
Are the STFTs moving constantly? That’s what they’re supposed to do, but as the sensors get old, the swings lessen, and move out of range, so perhaps thats the issue. The symptoms match the problem in this case.
Hi, both ltft are steady on -4.6, both stft are steady on 0. The only time they changed was as I turned the engine off, both graphs give a little squiggle. I will check it again tomorrow for longer, if the results are the same looks like I will have to change them, which I am not looking forward to, they are in such a awkward place.
No need to wait. Change them. They’re dead. If the STFT don’t move, they aren’t doing anything, they’re dead.
They should be moving up and down very often.
Anyone know what the correct part number is for the x300 oxygen sensor? I have bought two but when I have tried to remove the old ones they appear to be larger than the ones I have been supplied. the ones I bought have a 17mm nut but the ones on the car seem to be 22mm. Don’t want to remove the old ones until I am sure I have the correct replacement.
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