Stalling engine and hot starting. Help?

[nickh]

Hi all. This is my first post on here so hope someone can help? Have been searching through topics for an hour or two now but can't really find anything similar.

I have a 1994 S4 (brembo model). The first problem is its tendancy to stall when i come to a stop once it has warmed up properly. It doesn't happen all the time however,but particularily when braking hard to a standstill. If i dip the clutch in good time its usually ok, or use a little heel and toe-which i tend to do automatically now to avoid the problem!

This has become more of a problem recently, as now the car will not start again when it is hot. If i leave it for 10 to 15mins after a 'proper' run then it starts first time, but if i try it straight away-no chance! Its almost as if its out of fuel?

I have left the car running at home until its properly warmed up, fans cut in, turn it off, starts first time-but if i actually drive it up to temp. the problem occurs.

The stalling problem only started after my Lotus guys had it last August for some other work, and i got them to change the plugs and fuel filter while they had it (don't know if this is related?). Prior to this, i never had any problems and the car used to pop and bang nicely on over-run which doesn't happen anymore. They fitted plugs direct from Lotus parts list.

Apart from that, its a complete pig to drive at slow speed-in traffic, seems to mis-fire and 'runt' rather a lot.

Wondering if all these problems are related and get the feeling it could be something as simple as wrong grade plugs and a dodgy sensor somewhere??

Any suggestions please-i love the car to bits, but its starting to become a pain to drive and a bit too 'quirky' for its own good!!

Thanks in anticipation Nick.

[lotus4s]

I'd look at the IAC (idle air control) valve first as it can cause similar problems. Could possibly also be a weak fuel pump.

Freescan would probably narrow down the areas to look at for your problem. Do you have an ALDL cable. Do you have the Service Notes?

[nickh]

I don't have a cable but i have downloaded the parts catalogue/service notes if that's what you mean? It was suggested to me that the hot starting problem could be to do with the engine temp sensor?

Have to say i've read a lot about this freescan but really don't have a clue what it is Im used to looking after all my cars myself but not good with electrical stuff! You might think it would be easier to take it back to my Lotus guy, but im in N.Yorks and they are other side of Huddersfield so it means taking it over-getting a lift back home-then going back again the next week. And when you're at work all week and they finish at 12 on a Saturday, it becomes a proper ball-ache! Can't seem to find anyone else who specialises nearer to me??

[freshcut]

Freescan is just a program that runs on a computer, and interfaces with your cars ECM through a dedicated cable (usually serial or USB). The program basically receives data from the ECM on sensors and other data thats processed and gives you solid numbers that many on here can interpret to understand what is going on, whats normal, and what doesn't look quite right. It's very valuable since the ECM takes this information and using a table of values, calculates fuel delivery and engine load. If a sensor or couple of sensors are giving unusual readings that are still within a set parameter, the computer will either over or under compensate which leads to drivability issues. If the sensors are out of range, this will illuminate the MIL, so even if you don't have an engine light coming on, there still could be a problem.

[nickh]

Thanks for that explanation -so how/where do i get such a cable and presumably i need to download 'freescan' from somewhere?

[Bibs]

Cable

Freescan

[nickh]

I have access to the normal fault finding plug in hardware as used by most garages these days-would this give a similar result, or would it have to have specific Lotus software?

....just had a thought-recently fitted a new engine bay header tank, could i have disturbed something in the process? It was quite awkward to connect the bottom hose as there seems to be so much going on underneath it. The hot starting problem only started to occur after this.

Edited May 13, 2010 by nickh

[freshcut]

It's possible that it could be related. One thing that I learned over the years working as a tech is that anytime you make something worse, or cause a seemingly unrelated problem you should undo what you did prior to the new problem. In this case, I would remove the header tank and check that any plugs in the vicinity didn't inadvertainly become disconnected or have loosened. Even a disconnected/damaged vacuum line can cause similar symptoms. In the case of a damaged vacuum line it may have just enough leak to cause these symptoms but not cause enough of a drivability issue allowing the ECM to still see sensor readings (usually MAP or O2) within parameters therefore not trigger the MIL.

[nickh]

Thanks Blake-i fully intend to do that firstly (as soon as i find the time!!), and hope this leads to the hot start fault. That still leaves the stalling problem of course.

On that note-Where exactly does the ALDL cable plug in ? Had a quick look today behind the glove box and can only see a yellow plug hanging free, is that it? I know the service notes say where they are but the drawings aren't very clear and i have no idea about the one in the engine bay-where is this?

[freshcut]

It will plug into the ECM ALDL data port. Generally they're located under the dash typically under the steering wheel, or on the passenger side under the dash. Unfortunately I don't know where it is located on the S4, but the V8 has two, one located in the trunk near the battery, and one up front in the passenger side under the dash (right side of the cabin). I'm sure someone here can provide a specific location. It should be a rectangular 12 pin plug, two rows, 6 on each row.

[sailorbob]

On the S4 the cabin ALDL connector plugs into a holding socket on the back of the glove box when it's not in use.

Edited May 15, 2010 by sailorbob

[nickh]

Finally got round to updating!! Well after plenty of messing about with freescan/cables etc. etc. and being unable to get the download to even run, and visiting my local area group where i was ''sure'' to get the answer (not!), i re-traced my steps from fitting the header tank and checked the IAC valve as i think Jim suggested. When i came to undo it, i found it to be only ''finger tight''-so i removed it, cleaned the mating surfaces and refitted it using a small amount of sealent and tightened it up correctly and left it to dry a short while, and...................................................

problem solved

The car now drives smoother/better than it ever has done since i've owned it!!! Seems you were right Jim

Thanks to all for your help.