Idling When Cold - Revs Drop Then Stalls

[kingboyk 2]

I have a 1.6 GTi registered Jan 1990. The engine has just been rebuilt and I'm still in the 500 miles running-in period.

 

Engine sounds nice and sweet but I'm having a problem when its "cold" (I lost the engine at the traffic lights a couple of miles from home so its not just when stone cold, but it doesn't appear to be a problem when warm).

 

This week after starting and doing a very short run up the drive I let it idle with no throttle input. I could see the rev count gradually drop down (it never used to do this). It started around 1400. Within about a minute it was down to 1000. It dropped to 500 and the engine stalled. Miles has suggested replacing the oil breather pipes and filler pipe. I was just wondering if anyone has any other ideas? If changing those pipes is the likely fix where can I get them from?

 

Simple language please, I'm not at all mechanically minded!

[pug_ham 245 3 Cars]

The revs dropping is normal, it does this as the SAD closes but just not that low obviously. It could be your SAD is closing too soon

 

The last time I remember something similar with a car that struggled to idle suddenly for no apparent reason was a dead thriottle switch at closed throttle, there is a test procedure for them which is simple with a multimeter but access to the TPS pins isn't easy as they are down the front of the throttle body & accessed from underneath once the plug is removed, tbh its often easier to unbolt the tps from the throttle body to test imo.

 

The test is in Haynes & also I've posted it on here before.

 

The breather pipes can be bought from stew at baker BM who also gives a forum discount but they might just benefit from a thorough clean out if they aren't in bad condition.

 

g.

[kingboyk 2]

Thanks Graham. What's a SAD? Tried Googling it but couldn't find owt.

[S@m 156]

Supplementary Air Device - see here;

 

http://www.205gtidrivers.com/articles/e3-sad.html

 

Sam

[tom pug 2 1 Cars]

Maybe a problem with the air flow meter, if its reading incorrect air flow coinciding with the sad valve closing could lead to incorrect air/fuel mix

[jameswallace. 8]

this is the same as mine! just replaced the SAD and it went back to normal just got one from someone breaking their 205

[Tom Fenton 1,548]

Miles is spot on, don't go throwing new bits at it just yet, but get all the breather system pipes thoroughly cleaned out and make sure all joints are properly clipped. The throttle body itself is just as important to get clean, including all the passageways.

 

When working properly an 8v Jetronic 205 should do the following from cold. Start up quickly with no problem, should only need a couple of cranks. Idle about 1100 for the first few seconds, the rise up to a fast idle around 1400rpm. Then if left to idle it should gradually slow down to around 950rpm. Do not be tempted to try and set it any lower than this IMO.

 

I did some jobs on Dave_B on here's 205 GTI 1.6, as he came to pick it up I reversed it onto the drive, and left it running whilst we were having a chat about various things. It sat there and did exactly the sequence as described above. The main differences were to replace a couple of breather pipes, thoroughly clean out the throttle body, replace the pipe to the vac advance, and then set it up.

[kingboyk 2]

Thanks guys, printing this thread out for reference

[acox99 74 1 Cars]

Sorry to resurrect an old thread, but I've recently had to up the idle on mine to an indicated 1100 as I was having problems when the lights are on. It was idled go previously around 950/1k and when the electrical system is loaded up that it would idle around 8/850 and it was Dieing at junctions, sometimes it would dip right down and the ignition light would flicker, and sometimes stall , I also had a similar problem during the warmup period. It starts perfectly and idles, but I can't have it idling below 1100 now. Is it worth checking the tps, what do they usually idle at under load when hot?

[welshpug 1,666]

dont mess with the idle, replace the alternator!

[pug_ham 245 3 Cars]

When did you last give the throttle body & breathers a good clean out as mentioned above ?

 

If it was fine when you last set it up then most likely there is just a build up of dirt making it worse & misbehave like you discribe.

 

Check the tps by all means but don't condemn it without doing the simple test with a multimeter.

 

g

[acox99 74 1 Cars]

I replaced the alternator with a descent brand new branded alternator only a matter of weeks ago. It was the same before replacement, the original one seized. The whole induction system has been apart and cleaned throughly when I had the engine out to do the engine bay. It runs better now than it ever has, but it's obviously not quite right. Do jetronic cars dip before finding its natural idle when blipping the throttle, dipping the clutch or coming up to a junction or do they return to a steady idle. I think that's where my problem lies. I haven't had a good benchmark to try it against. It goes well it starts perfectly, hot or cold. Never hunts, it runs at just under 3% co so I'm not going to touch the afm. Temperature usually runs just under halfway on the gauge, on the line. I set it up by the book. Il test the tps with a multimeter, as it's the dipping in revs that's causing the stalling.

[nomis 12]

I have the idle problem, usually only just after starting up.

 

The car starts fine, but not only on the key, it needs blip of the throttle and then a few blips after that - otherwise it tends to either very slowly hunt up to sit at just 750 to 1000, or cuts out

 

Once on the move, I have to be a bit wary in the first few minutes as revs can drop right back down to below 500, lights flicker and it can cut out - this is usually when slowing to a halt, rather than pulling out.

It is exacerbated by speed bumps, a bump from going over them can trigger the light flicker and cut out.

 

Mine has been set up by a previous owner with a K&N induction kit.

 

It had a fair bit of work done to the engine before I got it at New Year and other than this runs absolutely fine

[acox99 74 1 Cars]

Sussed it, the throttle stop screw was holding the butterfly open, wound that out until the butterfly was shut and the screw was just coming to rest against the stop then reset the idle and the tps, it's now running better the ever idled get at 1400 cold and coming down to 1000 warm. The stalling has stopped and with electrics on its dropping to 8/850 and doesn't stall.

[welshpug 1,666]

thats probably a tad too tight, you should be using the idle air screw to adjust it after setting the base throttle opening

[Tom Fenton 1,548]

I have always found that will make the stalling when dipping the clutch coming to a standstill really bad. Reason being you all of a sudden shut the throttle and dip the clutch. Revs drop quickly as does the airflow through both the closed butterfly and the bypass passage. The air needs to start to flow again quickly otherwise the engine cuts out. If it has to do this via the bypass port then in my experience often this doesn't happen fast enough and the engine dies. All the ones I have worked on usually end up needing the throttle butterfly closed setting opening up a touch. Usually over the years the head of the stop screw mushrooms over a touch meaning the butterfly is slightly too closed from where it should be. Clean out the throttle body until spotless. Open up the butterfly a touch, then reset the idle switch. Then with it HOT adjust the bypass screw down to about a 950rpm idle. Then they usually behave much better and won't cut out at junctions whilst warming up and not yet properly hot.

[acox99 74 1 Cars]

Thank you. its all spotlessly clean already, Everything was cleaned in a parts wash tank over winter, and checked over.

 

I opened it slightly as you say and adjusted the idle using the air bypass, it behaved fine on the way home tonight. I know clockwork injection is never perfect but it seemed a lot smoother and less jerky on light throttle, seeing as it's all original and 100k old it's not bad.

[nomis 12]

How easy is it to clean the throttle body etc?

Bearing in mind I'm a complete novice.