[Mk2] [NA] Poor MPG, maybe running rich and inconsistent idle

[jem]

Since I bought my Rev 3 NA a few weeks ago I've is averaged 22mpg and the tail pipes look very black inside (I'm getting about 230 miles from full to the light).

I've changed the following recently with no improvement:

New Plugs,
New Leads,
New cap and arm,
K&N 57i intake
Blueflame exhaust including De-cat.

The engine makes what feels like good power doesn't miss a beat and on the whole runs very well indeed. But along with the poor MPG, the idle often drops very low, sometimes too low and the engine stalls. It will idle low when the engine is stone cold, it's ok when warmish and will again idle low when fully warm. But it's inconsistent one set of lights it will be fine, then the next it will idle low and cut out.

I'm not sure if the idle and the poor MPG are connected, but has anyone got any pointers for what to look for?

Thank in advance for your replies.

[Turbocarl]

Have you checked for any error codes?

[jem]

Not yet, how do I do that?

[Quigonjay]

http://www.ayrpark.plus.com/errorcodes.html

just bridge the terminals with a paperclip
i'd guess at the o2 sensor

[jem]

Thanks, checked yesterday and no error codes.

However today I took the throttle body off, took the idle speed control valve off and gave it a good clean in carb cleaner and the a good squirt of WD40 to lube it up. But it all back on and it made no difference at all. But once I got home from work I disconnected the battery for a few minutes to reset the ECU and now the idle speed is perfect

Not sure if the MPG is any better yet as I've not done enough miles.

[jonboy2199]

Failing that mate I had the same problem on mine and it was the O2 sensor as mentioned earlier,swapped it out and happy days

[jem]

Well the idle is perfect now, but the mpg is still poor, so going to chance the O2 sensor.

[jem]

I've fitted a new O2 sensor and reset the ECU at the same time, and my MPG is still very poor, if not worse at about 20mpg

[jem]

Well going to check the ignition and cam timing when I get a chance.

Any other ideas?

[jem]

Still trying to get to the bottom of this.

I'm now starting to think maybe MAP sensor or ECU engine temp sensor. Or something really stupid like someone in the past changing the injectors and putting bigger injectors in.

So is it likely be a dodgy MAP sensor?

Is the ecu engine temp sensor a different one to the temp gauge on the dash, as that works fine?

Are the injectors on a REV3 NA normally lime green?

And lastly I have found this connector which is not connected to anything. What is it and what if anything should it be connected to? I've drawn a red line to show where the wire runs, this is looking down into the engine bay from the drivers side.

[jem]

Anyone?

[tranx]

If it's any help that wire doesn't connect to anything on my Rev2 N/A either. There are 3 connectors so far I've found with nothing on them.

[toxo]

That wire is for the aircon magnetic clutch - if your car doesn't have aircon then it won't connect to anything.

Yes, the ECU coolant sensor and the dash coolant sensor are different. See http://www.imoc.co.uk/forums/viewtopic. ... light=2250

[jem]

Cheers guys, sounds like it could be worth my while changing it then. Where is it located on a REV3 NA?

I checked the MAP sensor this afternoon and it seems fine reading about 2volts at cold idle and going upto about 3.7 volts if you blip the throttle and then around 1.7 volts as the revs drop back to idle.

I do have concerns about the cam timing though. With the engine at TDC, the marks on the cam pulleys were at 12 o'clock in relation to the engine on the exhaust cam and about 5° counter clockwise for the inlet cam ( something like this \ |
So it looked like the inlet cam was a tooth retarded. I've slipped the belt off and set it with both cam pulley marks at 12 o'clock (like this | | ), then gave the engine a few turns and double checked. But I suspect that if they are lined up with the marks on the back plate they should splayed out by about 10° something like this \ /

I didn't know there were marks on the black plate until I did a search on here after putting it all back together.

I'm going to have to take the belt of and set it correctly to be sure, then double check the ignition timing. While I'm in there I may as well put a new belt on, it looks fine but I have no idea how old it is.

[toxo]

I'd assume same place as the turbo, in the coolant neck near the distributor.

[jem]

Cheers I did think I saw one there, just wasn't sure if it was for the ECU of the gauge.

[toxo]

Gauge one is boot side, ECU one is cabin side (I think). If it's the same as on the turbo you need a 19mm deep socket, and don't forget the new crush washer!

[jem]

Well I changed the engine coolant sensor for the ECU this evening before the 25 mile drive home. The difference is really noticeable! Before the midrange was flat and low down the engine felt gutless. Was fine at high revs though, or so I thought. Not it seems to pull convincingly from 2,000rpm and really comes on song about 4,000rpm and goes nuts when the ACIS changes. So seems likely this has been the cause of my crap MPG.

I looked at Autodata at work today and that suggests the cam timing is correct. But to be sure, and for piece of mind, I'm going to change the belt on Saturday. Then recheck the ignition timing and enjoy.............hopefully!

[smig]

Is this a dealer part?, do you have a part number?, how much?
Cheers

[toxo]

Sensor is 89422-35010 £39.91 + vat
Crush washer is 90430-12005 79p + vat

Or pattern sensor from Camskill is £15 + vat

Those parts are all for the turbo, dunno if it's the same for the N/A. Maybe someone else can confirm!