Holyman007

iTrader: (1)

Hey guys,

I've searched everywhere and anywhere and I can't find the answer to my problem. Before I go back to the dealer and get charged for more diagnostic fees, I want to see if anyone has input on this weird problem.

My car is a 2005 RX-8 AT just to be clear

Just a little background story, I was having trouble starting a couple months ago. Turned out to be low compression which was replaced by a mazda dealer. Before I went to the dealer, I changed plugs, coils, wires, and engine mounts (because of vibration). Everything seemed fine besides the hard start and bad mileage.

Right before I went to get my engine replaced, I was already starting to experience this problem (I was thinking it was part of the engine compression problem). After I got the car back, turns out the problem is still there but the new engine started much faster and had a lot more low end power so I'm guessing its something other than the engine.

----------------------

The problem:

In 3rd or 4th gear just cruising (It's an auto), whenever I put the SLIGHTEST touch to the accelerator, the rpm will go up and then drop sharply similar to loss of power.

Then, if I put a bit more pressure on the accelerator, the rpm will shoot back up and continue as normal. I have tested this out repeatedly and it happens everytime at any RPM (take foot off pedal completely and slightly press it).

If I press on the pedal harder that just a slight touch (about half open throttle), it will sometimes act normally and sometimes stutter a bit before accelerating normally.

However in 1st or 2nd gear, this doesn't happen and the power is there all the way to redline.

----------

To see if it was anything wrong with the ignition system again, I switched the new coils with the old coils and tested the resistance of the coils. All of them seemed fine.

I switched the wires out. No change

I took the CAT off to see if it was clogged or failing. Both honeycombs were there and in great condition. O2 sensor was cleaned. No change

MAF and throttle body was cleaned multiple times before and after the engine swap. No change

ECU reset after all this (battery unplug for 30 min, odo hold reset, 20 time brake stomp). Nothing

Tested the SSV with my hand. Moves freely with a little squeaking although this doesnt seem like stuck SSV anyways because it's happening at any rpm, usually low.

I was thinking it could be a vacuum leak but on the dealer sheet, they did a vacuum test after the new engine and confirmed no leaks.

I haven't checked the fuel injectors (could it be clogged a bit?) but wouldn't the dealer have seen/checked it when installing new engine?

---------

Thanks for taking the time to read all this lol, I don't want to miss anything.

If anyone has ANY idea even where to start looking for the problem, it would be greatly appreciated.

______________________________________________
EDIT: Putting video of the problem in

Be sure to have annotations on and volume up to hear the engine rev.
The problem is very clear starting around the 1:20 mark when I'm in 4th gear.

tza0001

iTrader: (2)

OP there is one thing I have trouble understanding in your thread. Perhaps I am reading it wrong...How did the dealer take care of the low compression? Did the dealer replaced your engine? Have you checked your fuel pump?

Holyman007

iTrader: (1)

Yes the dealer replaced the engine.
I'm reading up on the fuel pump assembly now but doesn't seem like the symptoms I'm having.

Could something be semi-clogged so when I'm pushing lightly on the throttle, it stutters but when I'm more than half open throttle, it operates fine?

Mazurfer

This is purely a guess.
Could it be the Throttle Position Sensor or Throttle Body Butterfly itself?


Throttle Body can be checked easily.
Remove the Airbox and neck from the throttle body.
Leave the throttle body intact and electrical connected.
You're going to need someone to watch or to operate the gas pedal.
Turn the ignition ON.
Push down slowly on the accelerator pedal and watch the butterfly in the throttle body. Does it operate smoothly? Opening and closing?
Vary the pedal operation and look for any skips or hesitations in the butterflies movement. It should be smooth opening and closing.
This will verify if the issue is the throttle body or not.

Worth a shot.

Holyman007

iTrader: (1)

Thanks!
I'll give that a shot, I may have overlooked that since I sprayed a bunch of throttle body cleaner in there and didn't give it a second thought.

Is there a spring or nut or a bearing that could cause it to get stuck? If it is causing the erratic throttle, maybe I just need to WD-40 or clean out the gunk out of somewhere although I did spray the inside with the cleaner.

wcs

iTrader: (2)

Its electronic. If I'm following the conversation.

Holyman007

iTrader: (1)

Are you saying its probably a dirty or fouled throttle sensor? Or that its the ecu sending a bad signal from the accelerator pedal?

One thing I forgot to mention before is that I also cleaned the ESS but it didn't solve the problem. It was pretty clean from what I could see.

Holyman007

iTrader: (1)

Alright, I check the throttle body valve with the key switch in the "on" position. Seems like it doesn't open when the pedal is depressed lightly and only opens when it is half to wide open throttle.

Not sure if this is normal? It is pretty smooth opening at half to wide. I do have a couple videos, I just have to upload them.

Also, I took the car for a ride and sure enough the problem is still there. I also took a video of the problem.
I'll put annotations hopefully at the right times when I am depressing the accelerator lightly.

Holyman007

iTrader: (1)

Alright, I uploaded the videos. Be sure to have annotations on and volume up to hear the engine rev.
The problem is very clear starting around the 1:20 mark when I'm in 4th gear.


And the throttle body valve:


So I've read up a bit more on some other car forums after searching on google "rpm drop and rise under light throttle."

The most likely problems seems like its either a pressure leak somewhere, extremely clogged throttle body or valve not opening properly preventing air intake at low rpm, or something with the torque converter (torque lockup?)

Would a malfunctioning MAF cause this? I'm thinking of just buying a new MAF and throttle body to rule out those options but maybe I should just bring it to the dealer...

Mazurfer

If you intend on doing this, use throttle body cleaner and wipe the areas where the butterfly pivots and also where it comes to rest when close. By that I mean both sides of the little ridge that it comes to rest on. Work the butterfly manually when doing this.

Mazurfer

Not sure about you comments in the butterfly valve video as to when it opens or closes and with how much throttle, but see all that crap at about the 4 o'clock position in your video.......................clean that stuff out of there with throttle body cleaner and a rag.

Unfortunately, I'm not a mechanic and can't tell you that this is even likely a cause or not, but.................My car has somewhat acted the way you describe if it gets really sticky.

Also, there is a throttle body position sensor that may need to be looked into.

Sure a MAF could cause it, but I wouldn't go spend money on a new one until you know for sure.

Oh....................are you stock as far as the air intake goes? If not, then check that the VFAD nipple cap didn't fall off.

Holyman007

iTrader: (1)

Seems like the butterfly valve doesn't even open unless its at more than half pressure on the accelerator which are the only two times it opens in the video.
In between, I'm tapping very lightly on the pedal (which is when the problem occurs) but the valve doesn't move.

I do have stock intake and couldn't find the VFAD cap you mentioned.

I'll try spraying more throttle body cleaner in there and wiping it down thoroughly. Maybe I need to take the whole thing off and clean it completely.

Where is the Throttle sensor located?

Cliffjumper126

You don't have a VFAD because your car is an automatic (4 port)

Holyman007

iTrader: (1)

Alright,

So I took off the throttle body and scrubbed all the oil deposits off it.
The entire intake system is clean now besides the air filter which I'll be replacing in the next couple days.
It doesn't look that dirty but looks can be deceiving. Would a clogged or semi-clogged filter cause this problem?

I'm also noticing a large drop in fuel economy (around 12 mpg in city and 16 mpg on highway) according to fuelly.

My options now are to check the electronic diagnostics (would a accessport be able to check all the sensors?), check all the vacuum lines (can't hear a leak), check SSV (but I seafoamed before engine replacement), fuel pump and fuel injectors.

Would a bad front O2 sensor cause this? I know its known to cause bad fuel mileage.

Thanks for all your help.

Bulletshinka123

Im having the same problem with the same exact car and i just wish someone would help i cant find an answer anywhere. I ddnt clean my throttle body yet but i will get on that and see if it makes any difference