m20 flat spot

[mrb27]

Hi all, another tuning question
my 2.7 cabbie has a terrible flat spot when you put your foot down, it cough's, revs drop a tad then picks up, doesn't seem to matter what it is currently revving at. if you press the throttle slowly it revs ok, but stamp on it and that's your lot.. revs drop before picking up with a 'cough'.

Its a nightmare when changing gear not a pleasure to drive anymore..
Might also be worth note that it idles high. around 900-1k mostly.

I have had a read through the tuning blog but I don't have any test equipment, the blue sensor has been replaced, have swapped out ecu and also the afm, checked for air leaks but nothing.. still the same

Any ideas?

[maggspower]

Check again for air leaks, the tube between the block and inlet, the bung on the throttle body are two favorites for leaks.

[Speedtouch]

Sounds like your throttle position switch (TPS) may need cleaning out and resetting:

http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

[Grrrmachine]

I'd go for throttle position switch too.

[mrb27]

ok great, ill check both out, the tube between the block and inlet you mean the metal one with rubber seals on each end? with the tps, ive cleaned it out many times now, might just grab a new one. it does feel like an air leak but most of the pipes are new so none are cracked etc. was just wondering if crank sensor or broken down wire could be the cause

rely need to get it sorted though, its getting worse and its not fun to drive anymore..

[Brianmoooore]

Combination of TPS, minor air leaks, and injectors long past their best is the usual cause of this kind of problem.
It's the adjustment of the TPS that's important, not just that it actually works.

[mrb27]

injectors were done by injectortune a few months back so they should be fine. with regards to the tps, I need the 'click' to be as soon as possible once I start to move the throttle so I understand, which is the case with mine.

[Speedtouch]

Ah, but have you used a multimeter to confirm the switch is actually working?

[mrb27]

no, I don't have any testing equipment

[Speedtouch]

You could rig up a test lamp circuit to the switch quite easily; if the battery is in the front of your cab, you could use that to power it...

All that is required is a very simple series circuit such as this:

[miniblob]

Or £8.99 will get you a multimeter from maplin!!!

[mrb27]

Or £8.99 will get you a multimeter from maplin!!!

Or that

But ok, so the lamp would be on until I open the switch, when it clicks the light should go off. easy enough. ill give the switch a good clean and test it over the weekend, need to do a few other jobs so ill check for air leaks while im there.

Could the ICV play a part in this?

[Speedtouch]

Doubtful, but it wouldn't hurt to clean it out.

Try spraying WD40 around the inlet manifold-to-head joint with the engine idling; if it briefly raises the idle speed, you have a gasket leak.

[mrb27]

ok, its frustrating as ive rebuilt the top end, had everything out (exept the block) when I did the head gasket. I thought the flat spot would be cured as I replaced all the vac pipes etc, new gaskets but no..

but ill try the tps and check for leaks again at the weekend, ill keep posted

[Speedtouch]

I would also carry out a compression test to ensure all six pots are giving roughly equal pressures of at least 150psi or so.

[ah]

Is your fault anything like this

[mrb27]

yes very similar, but my engine does not sound nearly as bad as that one

But yes, if i hit the throttle quick the revs do drop. i have not had the chance to have a look at the tps but does make sense that the tps is at fault.
If i hold the revs at say 1200 rpm and hit the throttle the response is instant, only coughs/drops when pulling the throttle off the switching point.

[ah]

If you find out what's wrong with car could you please let me know as it might help me to find my year and half fault on mine,believe me I tryed nearly everything.my fault is exactly the same as the YouTube clip,among other symtoms.