Nissan 1.6 '96 fast idling problem

If I were you, then the first thing to do is to clean out the throttle valve assembly, both sides.

Also make sure that the throttle cable has enough slack.

MrCheerful

Doubt it's the MAF or the TPS, sounds like a sticky throttle body oridle valve

Sounds like either a sticking throttle via the cable or sticking shaft itself or if this model uses one- a failing wax stat fast idler.

Tim..

I've had a fiddle, please bare with me as I'm not a mechanic.. after removing the air filter housing I had a look at the 'upper' part of the air intake and it seems fairly clean. I sprayed some carb cleaner on the throttle valve, but it seems okay to me, and it's definately not the throttle cable itself.

After giving it some cleaning with the carb cleaner it's made no difference. However, I've returned to it today for another look.

With the engine off, I opened the throttle valve fully and took a peek inside with a torch. The inner (lower?) chamber looked 'caked' in carbon deposits (I presume thats what they are) with a few bits of bare metal showing where I presume my previous cleaning attempt managed to get to.

I've given it a few squirts of the carb cleaner, turned it over, then repeated and have manage to clean a fair amount of the crap away, but this doesn't rectify the problem, it may only give me better efficiency in doing that.

Another thing I did (while the idling was stuck 'high' at about 1200 rpms) was to unplug the AAC. As soon as I did that the idling returned to normal - is the AAC the most likely culprit or is it linked to something else further down the line?

I've also noticed the following issues that may be significant....

1. When I start the car first thing it goes straight up to around

1500rpms without any touch of the accelerator. Granted it is winter, but it's high for cold idle. I think the car has the wax stat, at least there is a device mounted next to the throttle cable spring that looks like it moves a lever or arm when a small column rises and pushes against the throttle (I presume it expands when hot thus it pushes against a lever that moves away from the throttle assembly, in this case it lowers the revs when the engine is warm).

1. If I 'trundle' along in very slow traffic using momentum and a low gear (around 1000rpms), and no touch of gas, if I then dip the clutch to change gear or stop it will sometimes rise up straight away to

1200/1500 rpms.

1. This is a really annoying one, I'm sure its related... more noticeable in low gears. If I'm travelling slowly or in either 1st,

2nd or 3rd, when I come off the gas it almost seems like the car 'seizes up' as though the fuel is being cut very quickly to idle, and it's also as though the accelerator is 'bouncing' (am I making sense?) :). I have to use a combination of dipping the clutch to take the edge off it, or be extremely slow when taking my foot off the gas... is this another problem or the same do you think?

Any help would be much appreciated, thanks.

Stuart.

All your symptoms are part and parcel of a caked up and or badly adjusted throttle / idle air control / throttle switch, which is giving you the jerky running and the sticking high revs.

The cold start revs of 1500 or so are correct though- this is the wax stat doing its job correctly.

You've made a good start of cleaning up the throttle body, get someone who is familiar with F.I. (japanesse if possible) systems to finish it off, clean out the idle control valve, check the throttle butterfly at rest position, the throttle posision sensor, and for any vacuum leaks around the inlet manifold.

Tim..

TPS, that's the potentiometer isn't it? I've seen somewhere that these can go iffy in Nissans, but you're right, it's time to get it checked properly rather than plod on without a clue. :)

Cheers,

Stu.