car starting badly. getting worse :(

dac69er

dac69er

Super Moderator
right just went out and measured the resistances after the car has stood overnight.

cts sensor at sensor: 4.7k ohms
cts sensor at ecu plug: 4.7k ohms
air temp sensor at sensor: 4.5k ohms

all seems good to me! seems pointless buying a sensor if the one there is fine surely?
 
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Texx

Texx

Super Moderator
dac69er said:
right just went out and measured the resistances after the car has stood overnight.

cts sensor at sensor: 4.7k ohms
cts sensor at eco plug: 4.7k ohms
air temp sensor at sensor: 4.5k ohms

all seems good to me! seems pointless buying a sensor if the one there is fine surely?
Click to expand...

I agree, those readings are as to be expected of a cold engine so shouldn't cause a starting issue.

Did you try and start the engine after taking those readings and the fault reoccurred?
 
Texx

Texx

Super Moderator
It's a bit of a long shot, but check the harness ground point on the intake manifold by the idle control valve is in good condition. Even add an additional wire linking that ground point to the body of the car.
 
dac69er

dac69er

Super Moderator
Texx said:
I agree, those readings are as to be expected of a cold engine so shouldn't cause a starting issue.

Did you try and start the engine after taking those readings and the fault reoccurred?
Click to expand...

yup, fault re-occured. only way to basically eliminate the problem is to hold the throttle slightly open just on initial start. it stutters a touch but fires ok and then idles spot on as before.

all the earths are good, have checked them. i could add a few extras in just to be sure i suppose!


im starting to think there is something wrong with the idle control valve under the inlet manifold, im wondering if its sticking or slightly blocked and not letting enough air to be pulsed in on cold start then after a few seconds it moves/clears and allows the correct amount of air in.

just a guess but running short on ideas!
ill try and whip it off next week!
 
Texx

Texx

Super Moderator
It would also be worth checking the ECU is receiving 12V (iirc it should come from the start position of the ignition switch) at the STA pin during engine cranking. When the ECU recieves 12V at the STA pin, it won't add any ignition advance and should also increase fuel injection volume to aid with engine starting.

It's another test that won't cost you anything. ;)
 
Texx

Texx

Super Moderator
dac69er said:
im starting to think there is something wrong with the idle control valve under the inlet manifold, im wondering if its sticking or slightly blocked and not letting enough air to be pulsed in on cold start then after a few seconds it moves/clears and allows the correct amount of air in.
Click to expand...

It's definitely a possibility as Fatman previously said. As you've got another known good car, it's got to be worth swapping them over.
 
dac69er

dac69er

Super Moderator
im not going to start messing about with parts like that off my good GT. that runs perfectly so dont want to bugger it up!

ill measure that 12v supply, but i imagine it will be fine.

ill check a few more things this week if i get the chance. can you get that idle control valve off without removing the inlet or tb?
 
Texx

Texx

Super Moderator
dac69er said:
no, not that one. ive replaced that one with a good one from dave burwash. my original one had 2 snapped fingers on the metal springy bit! made bugger all difference to the way the car started and run though!

im talking about the thermostatically controlled one underneath the throttle body.
Click to expand...

Ah! I'm with you now. :homer:

I don't think you'll get to the mounting screws without pulling the throttle body off.

You could try pulling the vacuum pipes off, but I'm not sure what that's going to prove.
 
dac69er

dac69er

Super Moderator
hmmm, ill have to have a quick look if it ever stops raining.

dont want to take too much off one evening as i need the car to get to work the next day.

bloody car! ill see what i can work out and report back if i get anywhere with it
 
Texx

Texx

Super Moderator
Theres also an idle-up VSV (which I think is what Fatman was actually referring to :eek:) most likely located at the bulkhead some where.
 
dac69er

dac69er

Super Moderator
Texx said:
Theres also an idle-up VSV (which I think is what Fatman was actually referring to :eek:) most likely located at the bulkhead some where.
Click to expand...

there are 2 solenoid valves linked in with the vac line on the tb that are mounted on the bulkhead. alot of people remove them to no ill effect so i dont really know if they would cause any problem? i was always under the impression they are related to the idle up when using the aircon?
 
G

Gtstu

Member +
dac69er said:
there are 2 solenoid valves linked in with the vac line on the tb that are mounted on the bulkhead. alot of people remove them to no ill effect so i dont really know if they would cause any problem? i was always under the impression they are related to the idle up when using the aircon?
Click to expand...

i removed mine and dont have any issues
 
Texx

Texx

Super Moderator
dac69er said:
there are 2 solenoid valves linked in with the vac line on the tb that are mounted on the bulkhead. alot of people remove them to no ill effect so i dont really know if they would cause any problem? i was always under the impression they are related to the idle up when using the aircon?
Click to expand...

If it's stuck open though, it may cause a cold start issue. It would be a bit like trying to start a cold carb engine with no choke. Just trying to throw up some ideas that might be worth checking out.

I'm not convinced with the ECT sensor being faulty, due to it giving a correct resistance reading when cold and the fact you have no cold running issue once the engine has started.

I've had this exact issue before and it would be good to try and get to the bottom of it as I'm sure it's likely to happen to me again.
 
dac69er

dac69er

Super Moderator
Texx said:
If it's stuck open though, it may cause a cold start issue. It would be a bit like trying to start a cold carb engine with no choke. Just trying to throw up some ideas that might be worth checking out.

I'm not convinced with the ECT sensor being faulty, due to it giving a correct resistance reading when cold and the fact you have no cold running issue once the engine has started.

I've had this exact issue before and it would be good to try and get to the bottom of it as I'm sure it's likely to happen to me again.
Click to expand...


my other GT has never had this problem, but on this Gt it just comes and goes. at the moment it is the worst its ever been and does it almost everytime. even when it does start ok it stutters a little bit.

ill check everything mate. ill connect the solenoid valves straight to the battery and make sure they open and close fine.

thanks for all the suggestions, looks like im going to have to cover pretty much everything to get to the bottom of this!
 
L

Lawrence

Member +
now that i think about it, i think ive experienced something like this, if i turn key to quickly it seems to struggle to start sometimes, then its start and run badly for a sec. I thought it was fuel pump not priming up quickernough. But just a thought.
 
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