Weird idle

jerdes · Postby **jerdes** » Wed Mar 30, 2011 5:47 pm

I bought my 1990 NA6 mx5 about two weeks ago now, it drove perfectly until just recently.

I noticed the car was struggling to start first go, but would start perfectly second go. Then at idle it would sit around 1.5k, after a bit then drop to around 750, and would start surging up and down.

Now the car struggles to start and when it does, the revs drop instantly down to like 500 and is really shaky, I have to keep the car alive by revving it a bit when trying to start it otherwise it will stall out.

I changed the spark plug leads today, found one of the leads I replaced had been taped up with red electrical tape and there was also some oil found on the end of the plug leads. After replacing the leads, the car still struggles to start and idle sits at 500.

What is wrong with it?

manga_blue · Postby **manga_blue** » Wed Mar 30, 2011 7:11 pm

Oil leak in the cam cover flooding the spark plug tubes? Maybe just need a new cam cover seal.

jerdes · Postby **jerdes** » Wed Mar 30, 2011 7:54 pm

Yeah I've read to fix up that oil leak, changing the valve cover gasket will do the trick.

Any thoughts on the idling issue? Just went out the car then, after it warms up, revs sit around the 1250 to 1500 range, car has still plenty of power. Going to try change the spark plugs tomorrow and see if that helps.

jerdes · Postby **jerdes** » Wed Mar 30, 2011 7:54 pm

Yeah I've read to fix up that oil leak, changing the valve cover gasket will do the trick.

Any thoughts on the idling issue? Just went out the car then, after it warms up, revs sit around the 1250 to 1500 range, car has still plenty of power. Going to try change the spark plugs tomorrow and see if that helps.

muzza2 · Postby **muzza2** » Wed Mar 30, 2011 11:39 pm

try changing the O2 sensor,
i've found that many idle issues have been corrected by replacing that.
otherwise normal stuff, plugs, leads, possibly need looking at the idle screw (but if it ran well before and not now, then probably not this)

also look at the air cleaner & "possibly" (although highly doubtful) old oil

Postby **Okibi** » Thu Mar 31, 2011 4:48 am

Does it run (and idle) fine once the car's warmed up?

jerdes · Postby **jerdes** » Thu Mar 31, 2011 9:11 am

It seems to idle better when the car has warmed up.

jerdes · Postby **jerdes** » Thu Mar 31, 2011 7:18 pm

Changed the spark plugs and o2 sensor today, there was a bit of oil in the 1st and 2nd spark plug chambers, on the outside.
Car still idles really low when cold, then when warm, idles around 1250-1500..

Any idea whats causing these idle issues?

jerdes · Postby **jerdes** » Sat Apr 02, 2011 4:26 pm

Attempted to check if any codes were popping up today, dash didn't show any codes at all..

Car still struggling to start without a little help from the accelerator, any one have any thoughts at all?

bensale · Postby **bensale** » Sat Apr 02, 2011 4:37 pm

Try bridging the ten and gnd terminals in the engine diagnostics box. How does this effect the idle? It could just be that the manual idle speed is out and needs adjusting.

Is the TPS plugged in? If it is unplug it and see what this does...

Final one is a bit of a long shot... Have a look at your pedal box... Is there any play in the box when you press the accelerator? Mine had a crack in it and every time I used the throttle it would move the box... This caused me a heap of idle issues as it changed the tension of the throttle cable giving me a very erratic idle speed depending on where the pedal was sitting.. There are a few pics of this half way down page 15 of my garage thread viewtopic.php?f=57&t=29464&start=210

jerdes · Postby **jerdes** » Sat Apr 02, 2011 5:13 pm

bensale wrote:Try bridging the ten and gnd terminals in the engine diagnostics box. How does this effect the idle? It could just be that the manual idle speed is out and needs adjusting.

Is the TPS plugged in? If it is unplug it and see what this does...

Final one is a bit of a long shot... Have a look at your pedal box... Is there any play in the box when you press the accelerator? Mine had a crack in it and every time I used the throttle it would move the box... This caused me a heap of idle issues as it changed the tension of the throttle cable giving me a very erratic idle speed depending on where the pedal was sitting.. There are a few pics of this half way down page 15 of my garage thread viewtopic.php?f=57&t=29464&start=210

Thanks for the reply mate,

Bridged the two terminals, idle stayed the same, around 500 and less when cold.
TPS was plugged in, unplugged it and idle was still the same.
After car warmed up, it started idling around 1500 and less.
I also tried combinations of both TPS unplugged and bridged, TPS plugged and bridged with no avail.
Also there doesn't seem to be any play in the pedal box..

This is so annoying..

bensale · Postby **bensale** » Sat Apr 02, 2011 5:37 pm

Drats... I've had a few idle issues over the years I've had the car... They were the three solutions to the problems I've had, manual idle speed, dodgy TPS and the pedal box. Your pedal box not having play is a good thing... I would take variable idle speed over changing one of them again...

Are you saying that the idle speed stayed the same both hot and cold when you bridged the terminals? So 500rpm when cold and 1500rpm when warn irrespective of whether or not the terminals were bridged..? That doesn't sound right as when you bridge the terminals the car should run at the manually set idle speed (around 850rpm).

jerdes · Postby **jerdes** » Sat Apr 02, 2011 5:44 pm

bensale wrote:Drats... I've had a few idle issues over the years I've had the car... They were the three solutions to the problems I've had, manual idle speed, dodgy TPS and the pedal box. Your pedal box not having play is a good thing... I would take variable idle speed over changing one of them again...

Are you saying that the idle speed stayed the same both hot and cold when you bridged the terminals? So 500rpm when cold and 1500rpm when warn irrespective of whether or not the terminals were bridged..? That doesn't sound right as when you bridge the terminals the car should run at the manually set idle speed (around 850rpm).

Yeah I remember reading through your build thread when I first got my car, I couldn't imagine trying to mess around with the pedal box.. Have no idea how you managed to fit your head underneath there ahah.

Yes.. that is correct.. I thought that was a little strange as well..

bensale · Postby **bensale** » Sat Apr 02, 2011 6:06 pm

Hmm, lets just say it didn't fit particularly well... I did take a lot of the car apart to make it a bit easier though...

I'm thrown by the idle speed not changing when you bridge the terminals and staying at 500-1500rpm...

Do you have a multimeter? It's maybe worth checking the TPS. Un plug it and put the multimeter on the bottom two pins, it should read closed circuit when it is closed and then read open circuit when you open the throttle so the screw is slightly off the stop tap. You can turn the TPS to adjust it.

jerdes · Postby **jerdes** » Mon Apr 04, 2011 8:55 pm

I took my car to a mates brother who owns his own workshop, he had a look at my car, pulled out a screwdriver and adjusted the idle.. Car idles perfect now..