Rolling idle, cycles hi to low

abrad

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#1
Make
Honda
Model
Accord
Year
2004
Miles
200,00
Engine
2.4
HI guys

Stepson is looking at buying the neighbors car for $200. It will be his first car.

A few known issues -
Rear brake(s) lock up when sitting. My thoughts are stuck caliper or the pads are getting jammed on the slider. Won't be the first time I've done that.

Neighbor started it up to take for a quick test run, when something blew and power steering was lost. When I checked it, I see LOTS of fluid down by the rack and pinion, so my guess would be it blew at the tie rod. I see no fluid on top, so not likely a hose. Won't be my first rodeo changing out one of those.

Now the interesting thing. We started the car up, and it starts fine, then it starts revving, dropping to normal, then continuing that cycle. Quick internet search shows either a stuck/sticking throttle plate (my guess seeing as the car has been sitting since August) or possibly a vacuum leak. Any ideas?

My stepson is already aware his hands will be getting dirty!!!
 

grcauto

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#3
Clean the throttle body good. Take it off to do it. Make it look like new.
 

abrad

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#4
Thanks guys. Talking with my neighbor and stepson I was guessing at some type of throttle control issue, or throttle position sensor issue. Even told the wife the first thing I would do is remove the throttle body and give it a good cleaning!
 

nickb2

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#5
Also, of note, some times cold soaking the IAC valve in some gunk or similar product overnight MAY, and I repeat, MAY, help solve, but mostly, this has been a honda plague and sometimes, on these cars, only thing left to do is verify the software, see of it is on latest version.

In the mitchel on demand section of top fixes for this problem, huge amounts of IAC valves were swapped out. As GRC mentioned, thoroughly cleaning out the entire unit/throttle body is essential, in most cases, that combined with a cold soak in product overnight usually does the trick.

Honda is hugely aware of this. I many cases, the PCM does not interpret well the IAC control values. The newest software version has a patch included specifically designed for this PID value mismatch for this type of problem.

Also, have you scanned the unit for any codes? If it is loping around, you may have a P0570 or similar set in background. If so, that would confirm that.

I went to bed early last night, so now awake at 3 am and had time to ponder this more. There is also a throttle linkage adjustment that may also help this issue. If it has gone out of alignment/adjustment, the dashpot values will have changed. A labscope also helps to see the duty cycle. But since most don't have a scope readily on hand, then a live data scanner is essential.

I think your model has a vacuum dashpot, plz confirm that. Applying vacuum there and monitor voltage. While monitoring voltage, slowly open throttle, voltage should go from 0.5v fully closed to 4.8v and should not show any glitches. If so, you will need to replace the TPS also as it most likely has a flat spot on the resistor.

All of these are very common problems to these engines of this era.

Sometimes I tend to go to far into a problem and confuse ppl. This is not by intent, but merely my assiduousness in wanting to provide the most info I can.
 

nickb2

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#7
Also of note, once the throttle body has been cleaned, a ECM idle relearn is needed. If the tps signal is out, sadly it is not serviceable/adjustable/removable on this engine. The unit as a whole needs to be replaced. At least that what is what honda says, but using a small dremel bit and slotting it like the old civics back in the day often tricked the ECU. This is a last ditch effort at this point and usually reserved for back yard stuff. :cool: Screenshot (50).png
 

nickb2

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#8
I love clones, every one here knows that. Plz check out this article. Note it supports all you will need such a idle relearn and probably also can flash to the newest version for the ECU. Sweet. http://blog.obdii365.com/2019/07/09/honda-diagnostic-system-hds-him-clone-any-good/

Although for some, 200$ for the gateway interface from teradyne may seem expensive, think about it. If you plan on keeping the car or buying others like it, it will most def be an investment. Most ppl I know stick to a brand.

Anyway, as usual, getting ahead of myself, I just love this trade. ;):bat:

http://www.obdii365.com/wholesale/honda-hds-him-diagnostic-tool-with-double-board.html

This double board really looks interesting. Claims to write memory for only a 100$. It does look cheap, but hey, if it works, why not?
 

billr

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#9
A bit off-topic, sorry...

What Teradyne are you referring to? I worked for Teradyne many years ago and would be surprised if they now had products for the auto industry.
 

nickb2

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#10
This one Bill. Teradyne GNA600 Kit (TDS35540402)

I don't know if it is the same company you had worked for, but it was made by "A" company called teradybe, was sold by snapon and others, but is discontinued but cloned and can be had for alot cheaper now. Again, quality suffers when cloned but still has OEM bi directional and all other goodies. As usual with these things, it does OBD2 regular can protocol, so also good for other car related diagnostics for all makes.

https://honda.snapon.com/HondaAcura/ItemDetail.aspx?itemId=39211325
 

nickb2

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#11
I think it (teradyne) is a semi conductor company, maybe they helped develop, I don't know. But some of the clones I have seen on e bay or amazone, ali blabla etc are going for about 200ish give or take. Paired with a laptop or tough pad etc, should work like a champ if chipset is any good.
 

nickb2

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#12
This link does show teradyne active in SOC or FLEX platforms in automotive, and we do see end products on this page with images of scanner such a mine and such, so the GNA kit is probably based on a teradyne SOC or similar, but I am way off being the specialist you were when working there. https://articles2.marketrealist.com/2015/01/teradynes-offerings-provide-value-end-user-markets/

Anyway, off to work. Also, got a nice gift yestarday, my boss paid for my personal scanner to be updated, it cost 900+$. So this morning, should be good for 2019. Sweet. Thx boss. ;)