Check Engine Light / O2 Sensor

Hi everyone,

So I have a 2002 TF160. When I first bought it in October last year, it hated idling at traffic lights. I would have to keep my foot on the gas just to keep the engine running otherwise it would idle below 700 and just drop and stall. Driving slowly in first gear (a car park for instance) was also always a bit of an experience, sometimes I would have to depress the clutch and rev the engine just to keep it afloat. So, I had the car fixed up in Cambridge and they fitted a new 'upstream O2 sensor'. That seemed to do the trick for some time although the engine light came back on pretty soon after, then it went off, then on, then off again...the car ran fine and with lockdowns etc. I was happy to save dealing with this for another day. Today seems to be that day!

The engine light has been off for a few weeks but came back on today. I was driving at around 20mph as it did and immediately the engine sounded unhappy. Approaching slower than 10mph speeds was tricky again, idling at traffic lights a constant battle with the throttle to keep the engine running. As soon as the car runs above 10mph it's absolutely fine - great actually! 

I haven't scanned the car just yet, will do tomorrow, but I scanned it a month ago, the last time the engine light came on, and had a P0135 - O2 Sensor Heater Circuit (Bank 1 Sensor 1)

I'm fairly new to cars but am super keen to learn as much as I can, so here are a few questions:
1) This is a fairly common problem apparently, does anyone have any tips, ideas?
2) Does this fault code correspond to the 'upstream O2 sensor' that was fixed or is this a different sensor?
3) Is there anything else I can check in the meantime to try and find the fault myself? (OBD2 scan incoming tomorrow)
4) Is this something that I could potentially try and fix myself (with enough patience..) or are problems like these best done straight at a workshop?

Thank you everyone for your time!

Hi, :welcome2:
The fault code does refer to the upstream sensor. It will remain on until it is cleared, so is probably from your earlier problem.
If there are no misfire fault codes or other sensor failure codes it suggests that the idle is out of wack.
Theoretically a low idle should prompt the idle control valve (Iacv)(aka the stepper motor) to try to lift the idle speed to prevent stalling.

So two possible problems 1. The iacv is not working. 2. The base idle speed is way too low.
The idle could be low from a restricted air flow, is the air filter good and clean? 
You can adjust the base idle with the set screw on the throttle body. Disconnect the iacv plug when the engine is up to temp.Check idle. Turn the screw a quarter turn at a time and recheck idle speed. Base idle should be 850-875rpm.  
Plug the iacv back in and observe the idle speed.  It should settle at 875-890 rpm.. If the iacv is working it may take a while to settle and change step several time over a few minutes.
If the final idle is way out., you may have to repeat the process until you have a stable idle in the 875-890 range.

If plugging the iacv in and out has no effect  the iacv may be duff. Sometimes cleaning it with carb. cleaner will free the  valve. If not replace it.

Thank you for your reply! That's an interesting idea, I was so focused on the 02 sensor I didn't really think of anything else.
I'm taking the car for a long drive now, then I'll scan it and that should give me a better idea of what's going on. Will update the thread in a few hours. 

Hi and welcome to the forum

What scanner are you using?

James

Hi everyone,

Apologies for keeping quiet the last few weeks, I do very much appreciate everyone's input and I think I've been able to narrow down the fault a bit recently. 

As David mentioned above, I now also think it's less likely to be the O2 sensor. The sensor was replaced back in November and the code was cleared at the time so it is a bit odd that it has returned, however, I think the computer might be misreading a problem and reverting back to the O2 sensor. I scanned the car and it still came up with P0135 and no other faults, using a cheap Bluetooth scanner and Torque Pro, not the best I know but all I have at the moment. 

So, what I have learned from driving the car around the city as well as on longer motorway stretches is that it runs absolutely fine when it's up and running. The problem exclusively exists when the engine is cold / at start-up that much is clear now. What happens at start up is that the engine starts rev hunting from around 400rpm-800rpm and then just dies down to 0 until it stalls. This all happens within a few seconds of start-up and then if I restart the car everything is fine. Sometimes when I notice it starting to complain I just turn the car off myself now and back on and then it's fine. What I have noticed is that it tends not to do this if I start the car and just let it sit there a bit first, but if I start and basically get going straight away it starts complaining. Especially, if my first move is to reverse out of a car park or similar - it basically always stalls on me if the first action is to reverse. 

So, this does seem like the IACV could be having difficulty. Here's a probably silly question mind you - I have a TF160 VVC - surely this also has an IACV but I can't find it neither does the workshop manual point one out? Am I missing something? 

Another thought is that it might be the alternator as the problem also exists more if I start the car with the radio and fan on at the same time, also I read somewhere that being in reverse puts extra load on the alternator but I'm not sure about that. For clarity, this car does not have air-con. 

Well, my next step would be to have a look at the IACV anyway...if only I could find it?


 

Obviously, as soon as I write to ask my questions I also find answers online. So the IACV is called Stepper Motor in this case, right? That would explain why I didn't find it. 

What is the difference between the plain 'stepper motor' and the 'stepper motor with housing' ? Is it possible to clean these on a TF or is it best to replace them?

Earlier  models had an iacv that split into the motor and the housing, making it easier to clean.
From, I think, the mk2 F,  the unit is one piece. It is possible to clean the later one using carb cleaner to remove the carbon build up.

If it is an idle problem it is always worth doing a Throttle Position Sensor reset as it is quick, easy and free. Might get lucky.

Warm up the engine to its normal operating temperature.
Switch the ignition to position 2 so that all the dash lights come on but don't start the engine up.
Press the accelerator down to the floor 5 times in 30 seconds.
Wait for 15 seconds.
Turn off the ignition.
The TPS has been re-set and the engine can now be re-started.

So, here is an update, and maybe someone can help shed some light on this. 

Although the problem used to appear when driving this is how it currently plays out:

For the last month or so, every single time I start the car, it idles for about 30 seconds, then starts shaking more and more until it finally just stalls or I usually take pity on it and turn it off myself. However, I then restart the car and it's as if nothing ever happened and it runs perfectly. I get incredible mileage (400 - 500 miles per tank on the motorway) so I'm positive the 02 sensor is fine even though that is the only fault that is being flagged.
It doesn't matter if the engine is cold, warm, halfway there, mornings, evenings, just arrived and driving off again....I always have to start the car twice. Sometimes I drive off at first go, and it's a struggle at higher revs - a restart then sorts it out. I've never knowingly witnessed a misfire but I think that's what it sounds and feels like. But why only at first go? 

Anyway, so then the engine light went off. Now suddenly the car is happy at the first go. Then the engine came back on..and I have to restart the thing each time. This went back and forth for about a week. 

Here is something else that I noticed today. My TF lives in a garage that I always reverse into. The fumes have always been quite strong whenever I drive off and I put that down to the exhausts not having anywhere to go so it's simply a strong smell. Today I started the car though, and the engine light didn't come up (nor did I have to restart the car). I let it idle for about a minute, then turned it off, got out, and was expecting to be hit by the nauseating smell of fumes but there was nothing...I did it again and still no smell. I usually hold my breath when closing the garage door it's so bad, but not today, and today the engine light was off. 

So, I have no idea what any of this means. I have a few things I want to try, starting from easiest to trickiest (for me anyway), so cleaning the air filter, maybe the spark plugs, maybe even the HT leads if it is a misfire? Not sure...but any suggestions would be super appreciated at this point if this rings a bell at all to anybody. 

Thanks everyone!

Did you check the base idle speed?

Total guess, but is there an issue with the engine temp sensor or its electrical connection? 

Hello I've had the same problem exactly and it was the O2 sensor pre cat. I replaced it with a non genuine MG one and that sorted the rough running/idle cut out issue but the EML kept coming on. In the end I swapped the new sensor for a genuine MG Rover one from Rimmers and my problem was solved. Make sure you have a genuine sensor these cars don't like the cheap copies.

Yeah I'll probably end up replacing the O2 sensor again eventually - for now I don't think it's that just because I replaced it last November and the code came back a month later..not going to lie, the symptoms do definitely fit that though.

Base idle speed seems ok to me, and I've just cleaned the air filter, (test drive coming up on Monday)

Next thing I want to check are the spark plugs, and ignition coils (my bet is on the ignition system to be honest)
So I took the cover off the engine thinking I'd know exactly what go expect from various videos etc and I was surprised to see this:

 


Can someone shed some light on this for me? I was expecting to see 4 'holes' for spark plugs etc but I'm seeing two at best and it just generally looks very different, or maybe not? 

Didn't want to start messing about without knowing as I don't want to add issues 

Thanks as always guys, appreciate everyone's time.