To you ECM gurus...

[Cruisergreg]

With the Lotus, I have a minor stumbling on decceleration and and an uneven idle. Done all the usual stuff - check for vacuum leaks, clean MAF, new plugs...

Here's the question: Last week the battery went dead. Really dead - 2.5 volts across the poles. New battery and the symptoms are much improved. Could super low voltage through the old battery while the engine is running upset the electronics, or would the alternator output pick up the slack?

 

[Beowulf]

(Speculation...)

On the 80-series ECM, if it loses power like during a battery exchange, the "learned" settings will be lost and the ECM has to go back through a re-learning process for a number of values. That process takes several start/stop cycles and most will notice things like a much higher idle and other anomalies. I would give it a couple of days before getting aggressive on other changes.

-Mike-

 

[Cruisergreg]

I would give it a couple of days before getting aggressive on other changes.

Its had 50 or 60 miles and probably 8 or 10 ignition cycles since new battery so I'm not expecting any additional improvement. The Lotus/Toyota chip tuners claim this generation of ECM learns what it needs to almost immediately.

There's really nothing else "aggressive" I can do except do a more detailed vacuum leak search and maybe check resistance across the idle controller terminals (it also performs the idle cut function which would explain the deccelleration issue if its bad). The super dead battery just had me wondering...

 

[pappy]

A failing Ox sensor can cause your symptoms. I think a sticking EGR can cause a bad idle.

 

[OGBeno]

A failing Ox sensor can cause your symptoms. I think a sticking EGR can cause a bad idle.

Neither will cause a rapidly failing battery though.

There's gotta be voltage loss/draw somewhere...

 

[Beowulf]

Neither will cause a rapidly failing battery though.

His complaint is rough idle and deceleration issues. The new battery is OK.

-Mike-

 

[Cruisergreg]

Neither will cause a rapidly failing battery though. There's gotta be voltage loss/draw somewhere...

There is a drain. The car has a complicated OEM alarm/immobilzation system (Cobra brand) that is known to drain the battery over a period of time if it sits (folks that put the cars to bed for the winter are recommended to use a tender). I can tell there is drain because, bear with me because it sounds strange, I put LED bulbs in the dome light some time ago and even when the car is off the light glows slightly (but not with incandescent bulbs). For whatever reason the security system is routed through the dome light circuit (no its not a Lucas system) but the draw has to be on the milliamp level. The car only sat for about 3 weeks without driving so I think it was just a faulty battery - only 6 months on a high-output 7 year battery (it was an Autozone unit so take that into consideration).

Yesterday I spent a little time tightening up a few obvious and accessible vacuum connections before going off to a meeting across town. I can say I didn't notice much of the previous issue, but then again I wasn't in diagnostic mode but focused on the meeting. Thte turbo produces a lot of heat so I'm thinking there are some brittle hoses. Fortunately there are fairly few hoses to check - not like a 2F, thank heaven.