Mk2 rev2 starting dead end

[English Bob]

So after a 200 mile drive and the car was purring beautifully I reversed onto the driveway and the revs were faltering up and down between 500 and 900, I revved the engine but it carried on doing it so I revved again up to around 3k and the engine died as soon as I took my foot off the pedal.
I started it again and it did exactly the same except after it died it would not start at all.
As I said over the last 5 years I have broken down a few times so I have replaced the following.
HT leads, coil, igniter, dizzy cap, plugs, ecu capacitors (have also tried a spare ecu)
Battery and vacuum lines.

I have checked the fuel pump with the diagnostic ports bridged and have fuel at the tank return pipe.
I have done a cam belt change and the timing is spot on (although it was 2 teeth out on the exhaust cam)

I have spark at all plugs
I have checked the throttle body plate is clean and opens ok.
And the air box is clear.

So I have fuel, spark and air
There are no fault codes showing on the diagnostics either so I was hoping it's not electrical?
I am truly at a loss as to what could be holding it off that would have failed with the engine running after an amazing drive?
If anyone can offer a suggestion of where to start looking next I would be so grateful!

[Snorkie]

Try a tiny squirt of brake cleaner in the throttle body as its cranking, (you need some one to turn the key while you spray into it).

This will at least tell you if your problem is fuel or electrical.

It should fire up and stall if its a fuel problem, or just crank if its electrical.

[English Bob]

Snorkie thanks for the reply I really appreciate it
So I took off the air box to spray some easy start in the throttle body and it started before I had the chance to spray anything
Happy and confused at the same time.
Before the original breakdown I had just filled up with fuel, maybe some debris restricting the filter and my pressure tests moved it? I really don't know?
I did notice that tick over was only at 500 not 900 which is new, also the engine coughs and stalls a little bit when blipping the accelerator gently.
Could this be a dizzy timing issue?
Anyway thanks again for taking the time to reply

[Snorkie]

I'm as confused as you are, I wonder if you have an air leak somewhere and when the engine is hot its too weak. Then when cold, the rich mixture is enough to make it run. Have a good look at all the vacuum pipes it only takes the smallest of holes to make the idle rough and stall.

[_Al_]

Measure up the air intake temperature sensor and coolant temp sensor for the ECU to ensure that they’re both within spec. Over time their response changes but the ECU won’t know that and won’t throw a code, it’ll just fuel for the wrong circumstances.

Likewise O2 sensor / knock sensor but harder to test

[benckj]

Could your crank pulley be slipping? Seem to recall another person having an issue like this and found the rubber deterioration between pulley & crank which resulted in random timing shifts especially when shut down.

[English Bob]

Measure up the air intake temperature sensor and coolant temp sensor for the ECU to ensure that they’re both within spec. Over time their response changes but the ECU won’t know that and won’t throw a code, it’ll just fuel for the wrong circumstances.

Likewise O2 sensor / knock sensor but harder to test

thanks , I have replaced the coolant temp sensor now,
the engine cranks but will not start still ,
the ecu is now giving code 24 on the diagnostics which I believe is the air intake sensor?
im sure I have started the engine with this sensor removed in the past?
also when it cranks there is a strange sucking sound at the end of the crank and a lot of smoke drifts out of the throttle body { which I have just cleaned out}

[BYRNEY1984]

Have you done a compression test. Because if you have smoke exiting the throttle body maybe you have an issue with your i take valves. Even with fuel and a spark you will need compression to run.

[English Bob]

No as far as I know it's never been tested.
I'll have a look into how to do that
I have since had the engine running but idle is 500 rpm and it stumbles when I rev before picking up.

[BYRNEY1984]

You’ll need a compression tester. Cheap enough nowadays. If it runs check what the fuel pressure is too.

[English Bob]

Brilliant I'll take a look at getting one of those
Fuel pressure is 38psi

[_Al_]

Measure up the air intake temperature sensor and coolant temp sensor for the ECU to ensure that they’re both within spec. Over time their response changes but the ECU won’t know that and won’t throw a code, it’ll just fuel for the wrong circumstances.

Likewise O2 sensor / knock sensor but harder to test

thanks , I have replaced the coolant temp sensor now,
the engine cranks but will not start still ,
the ecu is now giving code 24 on the diagnostics which I believe is the air intake sensor?
im sure I have started the engine with this sensor removed in the past?
also when it cranks there is a strange sucking sound at the end of the crank and a lot of smoke drifts out of the throttle body { which I have just cleaned out}

If you’ve started it without a sensor the code could be related to that. Clear the memory by disconnecting the battery and see if it returns after the next start up.

As noted above though, smoke from the inlet isn’t a sensor issue. Something bad has happened mechanically most likely.

[jimi]

IIRC it will run with the IAT disconnected but the mixture will be wrong (too rich)
If you haven't done so it might be worth checking the ECU capacitors

[_Al_]

ECU caps is a good shout, but they won’t cause smoke out of the manifold.

Don’t want to sound patronising, but how sure are you that the exhaust cam was 2 teeth out? What were the symptoms before you did the cam belt?