Weird idle issue with M20 325, little help?

Post Sat Nov 03, 2012 4:39 pm

Now, I'm fully aware our old E30s aren't the greatest when it comes to consistent idle. I've been doing quite a lot of Internet searching and can't find anyone with quite the same issue as me so I thought I'd pick the e30zones collective brain...

A run down of the issue: When starting the car sometimes it starts first fire, other times it will take a couple of attempts to get going. Whether this is something to do with the same issue I'm not sure. Once running it is initially okay, but when you rev the engine (either stationary or in drive) & release the throttle, the revs dip below the point of idle to and it cuts out.
It did do exactly the same thing around a month ago, but I simply removed the ICV cleaned it through and it was fine, idle was steady and didn't cut out.
So now it is doing the same as before I figured I would do some more tests to see why. I found the info about running a multimeter on the connectors and the readings are correct to spec, also tested the TPS which was correct. I checked over all vacuum piping and there are no splits or cracks anywhere so no air leaks I'm aware of.

Any thoughts? Anything else definitely worth checking?
The car is basically unusable at the minute as it just cuts out everytime I come to a stop! Frustrating!

Thanks again in advance
James

Post Sun Nov 04, 2012 11:00 am

Any ideas on this folks?

Been trawling through the depths of the internet and can't find much that I haven't already tried. Any input will be appreciated, would be nice to make it to work Monday! Haha, bloody cars

Post Sun Nov 04, 2012 2:31 pm

Blue temp sensor, have a look in the wiki.! This is the usual culprit for rough running from cold.

Post Sun Nov 04, 2012 3:09 pm

What engine ECU?
A M20 engine should idle as steady and with as little vibration as that in a Rolls Royce. If it doesn't, then there's a fault.

Post Mon Nov 05, 2012 7:08 pm

Problem solved, thanks for your replies. I limped it up to work and had the skilled guys at Dynotorque next door take a look. Had it back running all lovely again.

Thanks again or the replies

Post Mon Nov 05, 2012 8:36 pm

Just out of interest what was the problem?

Post Mon Nov 05, 2012 9:30 pm

Well I think it was a mixture of all the air pipes being a little clogged up, as a clean up helped a little. But the guys noticed that the smaller water hose that should run from the bottom of the thermostat to the throttle body and then continues on towards the back of the head area. they had been removed from the TB and joined together at some point by another garage at some point in its life. I'd seen the pipes joined together but because I'd not owned a 325 before I didn't know that that's not how they are meant to be!
Apparently they aid in correct idle from cold and through to normal running temps, so might explain some of the issues. They put them back in there rightful place and it seems to run sweet now. The idle is much steadier now and post revving returns straight back to around the 700/800rpm mark with no hunting. Hopefully this is the end of the issue

Post Tue Nov 06, 2012 10:07 am

Good stuff glad its sorted

Post Tue Nov 06, 2012 1:46 pm

The throttle body heater pipes are an anti icing device, which isn't really applicable in the more civilised parts of the UK, and wouldn't have any relevance to your problems.
The TB heater is a fairly common place for a M20 cooling system to leak however, so bare in mind that it may have been disconnected for that reason, and keep an eye on your coolant level for a while.

Post Tue Nov 06, 2012 6:17 pm

Brianmoooore wrote:The throttle body heater pipes are an anti icing device, which isn't really applicable in the more civilised parts of the UK, and wouldn't have any relevance to your problems.
The TB heater is a fairly common place for a M20 cooling system to leak however, so bare in mind that it may have been disconnected for that reason, and keep an eye on your coolant level for a while.

Thanks for the info. I built an AE86 corolla track car and the TB on that had the same system. But I have to admit, because I hadn't owned a 325 before I didn't realise that the way the pipe had been sleeved wasn't how it was meant to be on one of these.
Well, that's the only thing the guys changed with the car and it has fully resolved my idle issue. Before it was cutting out every single time I came to a stop, but now the idle is consistent, settles straight back to the usual spot after revving with no hunting.