Engine stumbling

[greyhound20]

Hi everyone,

My 1990 Esprit SE has a stumbling problem during idle. When I attempt to "blip" the throttle the engine RPMs actually decrease instead of increasing. If I push on the gas pedal very slowly the RPMs will increase but if I push on the pedal quickly, the RPMs decrease. The strange thing is that the car seems to drive fine. Slowly let up on the clutch, give it a little gas, and everything is fine. This only happens when the engine is idling.

Any thoughts?

Thanks,

Stephen

[Malc Holmes]

Your not alone!

I think a few of us have had this issue on SE's/S4's/GT3's. There have been masses of suggestions on what the cause could be. Throttle body air bypass not quite right, fuel pump not up to the job, leak in the inlet manifold, fuel pressure regulator needs replacing, plug leads shot, plugs NG... Up to now I have changed everything other than the throttle body settings and the fuel pressure reg and I still have a mild problem.

A good place to start has got to be getting yourself Freescan and getting some ECU data posted here or sent to a few of the experts who can understand it fully. If its an easy fault it will show up very clearly with freescan.

If I ever work out what is the root cause I will let you know. In the mean time, if you get it sorted please let me know!

Good luck

Malc Holmes

[greyhound20]

Your not alone!

I think a few of us have had this issue on SE's/S4's/GT3's. There have been masses of suggestions on what the cause could be. Throttle body air bypass not quite right, fuel pump not up to the job, leak in the inlet manifold, fuel pressure regulator needs replacing, plug leads shot, plugs NG... Up to now I have changed everything other than the throttle body settings and the fuel pressure reg and I still have a mild problem.

A good place to start has got to be getting yourself Freescan and getting some ECU data posted here or sent to a few of the experts who can understand it fully. If its an easy fault it will show up very clearly with freescan.

If I ever work out what is the root cause I will let you know. In the mean time, if you get it sorted please let me know!

Good luck

Malc Holmes

Hi Malc,

Thanks for the reply and the advice. I have downloaded Freescan but I am uncertain where the diagnostic port is. Where is it located? I would like to take a look at the port and see what kind of cable I need to get to plug in my laptop.

As soon as I know anything I will let you know.

Thanks again,

Stephen

[Artie]

Steph,

There are 2 ports, one should be under your passenger side glove box, look on LEW and you'll find it. The more accurate and reliable port is in the boot in the relay panel by the diagnostic light. You'll need a good Serial cable or USB interface to make the Freescan work right! Is your stumbling problem when cold or once warmed up? If it's on cold starts, this is because the IAC is fully open and way too much air is going in when you blip the throttle so it's tries to die.

Artie

[greyhound20]

Steph,

There are 2 ports, one should be under your passenger side glove box, look on LEW and you'll find it. The more accurate and reliable port is in the boot in the relay panel by the diagnostic light. You'll need a good Serial cable or USB interface to make the Freescan work right! Is your stumbling problem when cold or once warmed up? If it's on cold starts, this is because the IAC is fully open and way too much air is going in when you blip the throttle so it's tries to die.

Artie

Hi Artie,

Thanks for helping me locate the diagnostic ports. I'll post some data once I've taken it.

The stumbling problem occurs both when the engine is cold or warmed up. Its just when the car is idling and not in gear. The car idles fine, no worries, but once you press on the gas pedal it chokes the engine. When you shift into gear and ease on the gas the car seems ok. Its maxing out at about 0.4-0.5 Bar of boost pressure but other than that, it drives fine.

Thanks again for your help,

Stephen

[Artie]

I wonder if you have a significant vacuum leak. Post up some freescan logs asap so we can look over the values of the sensors etc. Check you map value in bar. At idle it should be around .45-.55, also your IAC may have lost it's park value, check to see that it starts at 170 and as the car warms up it should park at about 50.

Artie