Throttle control issues... And more! - LotusTalk - The Lotus Cars Community
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post #1 of 59 (permalink) Old 05-22-2018, 06:44 PM Thread Starter
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Throttle control issues... And more!

This issue had plagued me for months. This afternoon the car finally got so bad it's unsafe to operate on a public road. Where to begin...

Background: 2008 Elise SC (factory supercharged) Larini SC exhaust. Stock power train otherwise. Michigan car, now in California.

A few months ago on cold mornings the car started getting hard to start. Anything below about 50 and it would have idle issues. I'd never had that issue before. Soon the issue started resulting in failures to start and a P0638 code. After a ton of restarts eventually the car would idle and run. Before that it would surge between 1700 and 2000 rpm and have no throttle control. On any morning over 50 the problem would not occur at all. That's where we've been until this weekend.

It's been getting progressively worse and less temperature dependant over the last few days, along with a few new tricks! Upon first start today it did the usual cold weather thing, even though it was in the mid 60's. I finally got it running but it was loping like a cammed V8 and trying to stall. After about 5 minutes of driving it got better and drove fine.

Fast forward to after dinner, driving home. Started fine, only with a rough idle. Different idle though. Idle was normal but kept bogging, it would drop to about 600 every few seconds. Started driving home and on steady throttle input it would bog and the nose would dive, complete loss of power, but the exhaust is very loud in those moments like it's under tremendous load. It never got better. I finally made it to the freeway where the increased speed usually hides or cures the issue. At 65, steady throttle, it would bog, nose dive, and drop 5 to 10 mph while being very loud. Every time it would do this the temperature on the screen would drop to 158 then immediately climb back up to actual operating temperature. For the entire 20 mile freeway trip it did this every 5 seconds or so on average, but not rhythmically in any way. For one 2 or 3 second period I had no throttle at all and started moving over thinking it had died.

What I've fixed:
-Cleaned then replaced MAF
-Reseated all connectors on throttle body and ECU.
-Replaced entire intake assembly (mine was broken, thought maybe it was a leak of some sort.)
-Countless fault code checks and clears
-New catalytic converter (had a hard time getting it to pass smog when I brought it to California)
-Cleaned throttle body
-Checked all engine bay fuses

I think that's everything. I've run out of ideas and it's worse than ever.

Help?!

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post #2 of 59 (permalink) Old 05-22-2018, 07:29 PM
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Not sure if it would cause your symtoms, but check your drive-by-wire harness to verify that the connection is tight. It should be located in the top of the driver's side foot well. Refer to the factory wiring diagram.

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post #3 of 59 (permalink) Old 05-22-2018, 08:00 PM
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That's weird...does the rpm change when this happens? Does it drop then rev or drop or rev? Maybe the throttle (pedal) position sensor is going out? If it doesn't know where closed is it would make idle difficult and driving in general. Sounds like my car when I was tuning it and before I had the idle settings correct. Don't know if the torque app or other diagnostic apps will tell you throttle input percentage. That might be easy way to tell if they do...anyone else have ideas?
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post #4 of 59 (permalink) Old 05-22-2018, 08:32 PM
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The drive-by-wire throttle pedal is essentially a rheostat. Like any electrical component, it could malfunction and create weird effects on engine rpm inputs.

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post #5 of 59 (permalink) Old 05-23-2018, 02:30 AM
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I have a Go Point OBD reader, and it will show me the actual readings output by sensors and the throttle in real time. This is more useful than a code, as you can see if the O2 sensor is moving or zero volts, the throttle etc.
the temp drop is interesting. The dash is damped, I noticed this when the solder joint would go bad it takes time for the temp to go down. So it is probably seeing zero.

Bad harness connection or temp sender?

The computer thinking the coolant is -20F would make it run super rich at inappropriate times.
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post #6 of 59 (permalink) Old 05-23-2018, 03:47 AM Thread Starter
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I use the Torque app and it, too, does individual sensor readings. I'm curious if in it's graphing system I can get a percentage over time for throttle input. In the snapshots I've taken throttle is typically around 18% with no input from me, but it's hard to say if that's normal idle, or if it changes when the idle falters.

As for the temperature issue, I believe it's all related. The temperature display follows the pattern of the strange throttle/input/idle issues exactly. The car bogs and the temp display and to reset.

Other details I hadn't thought of before: I mentioned it took some time to pass smog. The shop claimed to have changed the cat and both o2 sensors then it passed. However, when I was doing my intake I noticed that the downstream o2 sensor has a CEL delete spacer on it. In my effort to tackle one issue at a time I set that aside in my mind, but I'm beginning to think that could be related. If it took that much to get rid of the CEL then maybe they were chasing a symptom and this is the actual issue.

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post #7 of 59 (permalink) Old 05-23-2018, 05:01 AM
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Watch the reading live to see how it varies.

clogged cat?

I am guessing more than one thing is going wrong
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post #8 of 59 (permalink) Old 05-23-2018, 05:08 AM Thread Starter
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Quote:
Originally Posted by exigegus View Post
Watch the reading live to see how it varies.

clogged cat?

I am guessing more than one thing is going wrong
I'm wondering if the shop that got it smog legal may have cheated me. There should be no reason a CEL eliminator would be needed on a factory cat with new o2 sensors.

Prior to their fix the car ran fine, just with a CEL. Even in the low 20s whole driving the car home from Michigan.

Today I'll check out the live changes to the ECU throttle input.

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post #9 of 59 (permalink) Old 05-23-2018, 05:15 AM
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When my throttle pedal wiring was unplugged it did that 1800-2000 RPM lope. Just a point for you. Also apparently the ecu plug can have the individual pins go bad, so that is something to look into maybe.

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post #10 of 59 (permalink) Old 05-23-2018, 06:32 AM
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I was having issues with my throttle as well recently. Even my MIL light was on with a code that pointed at a faulty throttle body control (DBW). I was also having intermittent ABS coming on issues.

I changed to a new battery 2weeks ago and the problems had not come back since. Fingers crossed.
Maybe worthwhile to check your battery.
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post #11 of 59 (permalink) Old 05-23-2018, 06:41 AM
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Quote:
Originally Posted by daehimeh View Post
I'm wondering if the shop that got it smog legal may have cheated me.
Yah think?
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post #12 of 59 (permalink) Old 05-23-2018, 07:36 AM Thread Starter
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Quote:
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I was having issues with my throttle as well recently. Even my MIL light was on with a code that pointed at a faulty throttle body control (DBW). I was also having intermittent ABS coming on issues.

I changed to a new battery 2weeks ago and the problems had not come back since. Fingers crossed.
Maybe worthwhile to check your battery.
I hope it's this simple. I've been meaning to fix some shoddy wiring in the trunk anyway, maybe this is the perfect time.

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post #13 of 59 (permalink) Old 05-23-2018, 08:30 AM
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Quote:
Originally Posted by kfennell View Post
When my throttle pedal wiring was unplugged it did that 1800-2000 RPM lope. Just a point for you. Also apparently the ecu plug can have the individual pins go bad, so that is something to look into maybe.
Can you expand on that? I'm having some electrical issues myself and am wondering what you mean by individual pins go bad? Pins on the ECU side or pins in the harness connector? What's the test and fix?
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post #14 of 59 (permalink) Old 05-23-2018, 09:25 AM
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Quote:
Originally Posted by LostPawn View Post
Can you expand on that? I'm having some electrical issues myself and am wondering what you mean by individual pins go bad? Pins on the ECU side or pins in the harness connector? What's the test and fix?
On the connector, you test by using a ecu pin and check there is friction (i got one from tj) and there is a lotus kit to repair. Mine were all fine and the problem was in there harness wire, was rubbed bare and grounded

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post #15 of 59 (permalink) Old 05-23-2018, 12:32 PM
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Quote:
Originally Posted by upgrader View Post
I was having issues with my throttle as well recently. Even my MIL light was on with a code that pointed at a faulty throttle body control (DBW). I was also having intermittent ABS coming on issues.

I changed to a new battery 2weeks ago and the problems had not come back since. Fingers crossed.
Maybe worthwhile to check your battery.
Sounds like the time to replace the battery did a full reset on your system.
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post #16 of 59 (permalink) Old 05-23-2018, 01:10 PM Thread Starter
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A quick update.
While I can't get Torque to log and spent the last 3 hours trying to figure out why, I did observe some sensor activity.
The throttle% when it's giving me issues is pegged at 18% regardless of idle RPM or pedal%. The idle during that time is irratic and low, occasionally stalling.
At some point, seemingly randomly, it will climb and do the bounce between 1700 and 2000RPM.
After countless restarts and attempts to provide throttle input it will finally just start normally and clear it's open codes. At this point the throttle% shows accurately and in line with what you'd expect with pedal input.
This seems to have little to no connection to coolant temp, oil temp, any of that.
I'm sure tomorrow when I waste another day trying to fix Torque I'll have more updates, but for now I'm frustrated to a point that I need to stop and do something else.

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post #17 of 59 (permalink) Old 05-23-2018, 01:33 PM
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After I had my '08 Exige S240 for about 2 years, the engine suddenly wouldn't idle and ran very erratically under throttle. It was still under warranty so I had it trailered to my local Lotus dealer. They cleaned/treated the throttle body and MAF electrical connectors with Stabilant 22, which seemed like voodoo to me, but the fact is it worked and the problem has never returned. Only downside is the cost, that stuff is expensive, but it's cheaper than throwing new parts at the problem.

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post #18 of 59 (permalink) Old 05-23-2018, 02:20 PM Thread Starter
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Yes, I'm an idiot and the attached files are of a huge size and I can't get a single program to resize them without cropping. These don't really shed any new light on the problem, but using Torque logs I was able to graph what the throttle is doing in relation to what the pedal is doing. One graph shows what it does when it's not working, the other shows what it does on a short drive while it is working. These two data sets were taken about 10 minutes apart after one of it's magical self-fixes.
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post #19 of 59 (permalink) Old 05-23-2018, 02:40 PM Thread Starter
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This is the comparison of the two data sets RPM. I cut most of the drive out to get their times roughly the same. Obviously the blue line is when i had no throttle control and the ECU didn't seem to know what the throttle was doing either. The red/orange line is when things were working mostly as they should.
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post #20 of 59 (permalink) Old 05-23-2018, 02:53 PM
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I am surprised no one else has said it, and maybe I am overlooking something, but it sounds like you need a new throttle position sensor. I believe they are a stock toyota part. I don't recommend trying to source one through Lotus.
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