Got IDLE BUMP?

CajunKenny

CajunKenny

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Nov 15, 2007
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I have owned two 7MGTE's and both had/have an idle bump. Every MK3 that I've been around has this issue except one and it is stock except for intake and 3" exhaust.

My current MK3 only does it once idle temp is reached. Cold starts idle like a dream...

I have seen vids of MK3's that don't have this problem; but, how'd they do it?

Barring the obvious things like, low compression on a cylinder, worn/leaking valve, etc... what causes this frustrating problem?

Have any of you resolved this issue?
 
CajunKenny

CajunKenny

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90T04;1613533 said:
I had that symptom and then it completely went away when I switched to the coil on plug setup
Click to expand...

I am currently running that setup. I will say that it drastically improved; but, she still bumps... Later, I'll try to post up a vid of my idle after it's at op temp.

destrux;1613534 said:
I've never owned a running 7M.
Click to expand...

Shhhhh... Don't say that too loud or else all the 1J guys will start mouthing off... ;)

Idle bump is a slight miss. Some cars do it worse than others.
 
S

stonecoretx

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Dec 21, 2009
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can be a number of things, coils,injectors,intake manifold..ect. i've had many cars with symptoms of rough idle or the occasional miss. i belive it's worse in cars without fuel injection, I had an Camaro back in the day with a 305, missed and shook like crazy. I looked at buying a ma70 a couple years back, the car looked like it was a pretty good shape eccept for the accordian hose had an air leak he tried to stop with duct tape (LOL) the entire car had a slight constant shake to it as it misfired, felt like a muscle car almost like a rough idle. I had a car do it really bad and it ended up being carbon build up in the intake manifold.

My current ma70 doesn't really do it but you can feel it in the shifter somtimes after shes warm.
 
Reiketsukan

Reiketsukan

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Apr 13, 2009
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My setup only got the "7M Pop" after I did the Lex/550 mod. It's just a light hiccup that happens occasionally at idle for whatever reason...
 
SupraSean

SupraSean

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Mar 3, 2009
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mine does it id say once every couple seconds at idle. ive never really worried about it too much. a miss is a miss, although when i changed out the silicone vac line i had running to the bov for a new rubber one, it decreased greatly, i need new plugs too so that is also a probability.
 
Nick M

Nick M

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I have never seen it. You should not have any hiccup like that with batch fire injection. Sequential cars do it more commonly. Meaning the lean miss you are describing.
 
CajunKenny

CajunKenny

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Poodles;1613637 said:
We used to call it the 7M hickup. I found improving the ground on my ignitor helped it a bit...
Click to expand...

This helped mine as well.

tekdeus;1613654 said:
Like an occasional exhaust pop? Mine does it.
Click to expand...

Yep. Well, sort of... When it happens, the tach dips slightly.

87M-GTE;1613710 said:
Boost leak?? TPS?

You said its only when the motor is warmed up.
Could be the cold start idle control

Sam
Click to expand...

TPS would be my only suspicion. I've checked it over meticulously though. ;)


Here is an op temp startup and idle. Unfortunately, it isn't doing it in this recording. I pulled the plugs and opened up the gap a bit. They are now at 28 thou. They were at 23 thou. That seems to have taken care of most of it.

[video=youtube;RRmTZ5sus4w]http://www.youtube.com/watch?v=RRmTZ5sus4w[/video]
 
grimreaper

grimreaper

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A big improvement on all things electrical was taking some old advice JJ does. Voltage drop test everything you can get to. I'll admit I didn't go as far as he did with a head light and all but the power and grounds definitely had room for improvement. Got rid of the dimming head lights when you role the windows down and a few other odd issues too.
Also keep in mind what JJ has posted on mkiiitech.com about the coils and their delicacy. Not hard to imagine a small short in the coil and the COP fixing the issue either..
 
Nick M

Nick M

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CajunKenny;1613453 said:
I have seen vids of MK3's that don't have this problem; but, how'd they do it?
Click to expand...

I guess I could have speculated based on how it is supposed to work. If you scale the signal from the AFM with the screw on the Lex meter, or a SAFC or something similar, you are lying to the ECU.

Back to the begining. As most of you know, the Lex meter works withe the screw all the way in to measure all the air. It is bigger than stock, so the Hz is slower. The larger injectors compensate this, and the A/F's are correct. But if you back that screw out, or scale with an SAFC, you are no longer in the correct range. You will be just a bit lean, and the car will have a light rumble, much like an old 5.0 Mustang.

I thought I read about the MAFT-Pro, that it can adjust ignition and fuel, much like e-manage. That would be best, aside from stock or stand alone. My car does not have the hiccup. I have a video about how they should sound in my build thread. I meant it as a joke over what I want my car to be like, and that is how Toyota built it. The air conditioner is on, and when I thought about it, I shut it off and you can see the perfect idle.
 
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CajunKenny

CajunKenny

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grim: I should definitely go through some of the wiring. The COP's most certainly helped. At this point, I think I'm being too picky. ;)

Nick: I've been lying to the ECU ever since I installed the Maft. :biglaugh: I will say that I have decided to leave closed loop operation to the ECU. I got tired of fighting it and honestly, wasn't winning. Now as far as WOT Open Loop operation goes.....I have the Maft set to tell the ECU to Sheeeeeeut UP! ;)

Converting to speed density seemed to substantially improve throttle response. An idle improvement was also noted.

I just hate having people admire my car and have them comment on my thumpy sound system. I have too much pride to admit to them that the stereo isn't on. ;)
 
Nick M

Nick M

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Something else to think about....Not having the front cat also puts a smidge more fuel in the muffler for a small muffler explosion. The cat won't burn it all, but it does seem like it should at idle.

Kenny, MAF translator or MAFT-Pro? I thought the Pro was only speed density.
 
CajunKenny

CajunKenny

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Nov 15, 2007
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Very true about the cat. Additionally, the cat will suppress little pop like nuances and such. So, not having one allows you to hear even the smallest of instabilities in idle.

There are different versions of "Translator". I have the "Translator Pro". It in itself is an AFC. Speed Density is requires add-ons. Speed Density Harness, AIT Sensor, Map Sensor, etc...

I ran it in AFC mode for the better part of a year and it was great! Speed Density is muuuuch nicer though. IMO, every MK3 should've come from the factory Speed Density. Not just the Turbo-A's.

Now if I owned a Turbo-A, I might feel differently about that statement. ;)
 
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