Just bought a 2005 rx8 with 150000kms on it. it was in limp mode due to a faulty OMP and i got it replaced at the mechanic's so the limp mode issue is resolved. However, the car runs super weirdly. When started up it runs fine for a minute or 2 then the idle starts fluctuating up and down. it keeps revving by itself. When driven it accelerates super rough, when the "powerband" hits at around 6-7 its like a rough change not a smooth acceleration. After a minute of driving the car shuts down anytime it is in neutral and not receiving gas (dies at idle) looking for any help possible, thank you! i'm a first time owner and feeling way in over my head. no rotary mechanics in my town so have to do it myself. The guy i bought it from did all his own work on it and put a new mazda crate engine in. its got like 20 kilometers on it.

 

Is there a check engine light? Do you have a way of checking the engine codes even if the light isnt illuminated?

Also research inspecing/replacing the neutral safety switch. Its relatively easy to find once under the car but will need some tools to replace it if it needs to be replaced. may just need the connectors checked/cleaned however.

You may have an issue with the ignition coils, spark plug wires, or spark plugs. Or a vacuum leak, injector wiring/injector issue, or a number of other possibilities. Hard to know when someone does their own work and then sells what they started leaving you (the new owner) with all their screw ups to find and no history to really work off of.

 

Hey RIcky!

Thank you very much for the reply,
There is a check engine light but the old owner told me it's because it has a cat delete on it. my mechanic said it was pulling some codes but nothing that can hint at the issue. I will check the codes myself when i get home tonight and reply again.

And i will look into the switch thanks!
Do you recommend i just go by elimination and start replacing the coils plugs etc...?

 

Get the codes. Elimination by replacement is a really expensive way to find out what wasn't the problem.

The abrupt jump at 6-7 could be the intake valves being midwired or vacuum misrouted. Google for the vacuum diagram and go over the previous owner's work.

Another common issue when installing engines is to mix up primary and secondary fuel injectors, which will cause issues like this. You'll need to get the UIM off to check that.

 

Hey RIcky!

Thank you very much for the reply,
There is a check engine light but the old owner told me it's because it has a cat delete on it. my mechanic said it was pulling some codes but nothing that can hint at the issue. I will check the codes myself when i get home tonight and reply again.

And i will look into the switch thanks!
Do you recommend i just go by elimination and start replacing the coils plugs etc...?

 

First off, welcome.

Knowledge is nearly everything when it comes to the rotary, sadly there are many people that fall into cars that are trap projects leftover from people who don't know better.

I suggest starting your knowledge by reading the sticky threads at the beginning of the new member section

Googling forum threads will help you, the search bar in the forum doesn't really work.
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It sounds like you are describing a few issues:

1. limp mode sounds like it was correctly addressed
2. The hunting/fluctuating idle
3. The non smooth powerband
4. Dying when idling hot.

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Do you have a stock intake? Hopefully you either have the stock or AEM intake. Otherwise I would suggest getting one.

Can you confirm that it is a new engine? Does it even look new? Paperwork of the purchase?

Does your car have any other modifications from stock? Ignition Coils? Catalytic converter?

What happens when you just start the car and let it idle for 15-20 mins? Time this please when you start to see hunting and then stalling?
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Issue #2 Hunting Idle

1. Try turning the key in the "on position" and press on the brake pedal 20 times until the oil pressure blips.........Report any changes, this
2. Get some Mass Air Flow sensor cleaner. You want to use this to clean both the MAF sensor in the intake and also clean the E-shaft (crankshaft) sensor on the front lower driver side of the engine. Plenty of Youtube vids on this. Repeat 20 brake stomps
3. Check for Vacuum leaks, the Rx8 has numerous Vac lines going all down the intake. Hunting Idle is a typical vac leak problem if the previous owner never connected something. To make it easier you could look up how to smoke your intake. Examples being the MAF itself can leak around it, the plastic elbows after the MAF, the Upper intake gaskets, The lower intake valve gaskets, the ports on the passenger side of the intake.....etc
4. Check the ignition system. First check the sparkplugs, they could be fouled, replace with the proper NGK leading and trailing plugs ~$80(yes two different kinds of plugs, the plug holes have an L and T marking on the engine). Then look into the ignition coils and wiring to be sure everything is hooked up right.
5. Check your fuel pump assembly
6. Check your engine compression. RotaryCompressionTester.com typically has sales on this forum, if you plan on keeping the car I would just buy one. Otherwise someone in your local area may have a tester you could borrow/rent. If you have low compression, the engine is toast. Possibly the previous owner tried rebuilding himself.

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Issue #3 Non Smooth Powerband

1. Again clean your MAF sensor and E-shaft sensor. If your MAF is dirty or has water in it typically your engine may bog like it hit an RPM limiter around 5-7k
2. Check your fuel pump, as these start to go you won't be able to climb to higher rpms
3. Check your vac solenoids that control the SSV and VDI valves. For this you have to take up to the Upper Intake. There are 3 solenoids on the back of the oil filler neck to check. Perhaps these are just hooked up wrong. However they also can break fairly easily.
4. While at the vac solenoids you should check the fuel injectors and wiring.
5. Check your Lower intake valves. There are 3 valves, the SSV, VDI, and APV. The SSV and VDI have actuators that you can try to move by hand. The APV has a little motor on the lower outer face of the Lower intake manifold. This motor could be taken off and you can try to turn the gear yourself, note the key marking on the gear. If the SSV and VDI are stuck with carbon you can take them out and clean them with brakeclean fairly easily.

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Issue #4 Dying at Hot Idle......After driving?

1. 5% chance vac leak
2. 5% ignition coils overheating
3. 10% chance the fuel pump may be overheating, full gas tank? Maybe bad pump
4. 80% chance Engine is losing compression when hot, bad engine. Or severely overheating your rotors due to an oil supply or oil cooling issue, Incorrect oil filter? >> bad engine

 

These are the codes i got!

 

These are the codes i got!

 

P0410 is your air pump not working. Could be as simple as a blown fuse or loose connector, or the previous owners removes it for some reason. Do you still have a catalytic converter? If you do, suggest fixing the pump if it's easy. But it's not the cause of your driveability problems.

P300/P301 are typical for poor ignition, clogged cat, bad MAF reading due to vacuum leak, aftermarket intake or oil in the intake. Check for those signs. When do the misfires happen? At idle, while driving at partial throttle or at full throttle? You'll know it's misfiring by the check engine light flashing.

The CAN / communication faults are not great signs. There's no good or common reason for them to happen. Clear all the codes and see which ones come back?

 

Hi! i don't think i have a catalytic converter, the previous owner said theres a 3" straight pipe with a exotic speed exhaust. And i opened the car up yesterday and the check engine was flashing when i was going super fast so i definitely think its a misfire. what should i do from here?

 

Definitely want to look at ignition coils/spark plugs/wires if they're of unknown age/condition.
what all modifications have been installed?

 

It is pretty common to see CAN communication errors with aftermarket scanners... most are because they use generic queries that are not ECU specific.

Delete them... they likely will come back when you scan again but don't usually indicate issues that will cause drivability concerns

 

Ohhh okay, what kind of scanner do you reccomend for most accurrate results? i live in a relativeley small town so i dont think we have any rotary gurus here

 

okay so what i know forsure is that theres a 3" straight pipe with exotic speed exhause, there is an AC Delete, A Mazdaspeed cold air intake, and the guy i bought it from said there's new plugs, wires, coils, but i'm not sure because it's showing that cylinder misfire code and i reset all the codes. check engine is not coming back on but its flashing during acceleration 100% plus its dying at idle like always and accelerating super weird. would a video help?

 

Basically use the one you have and just ignore the U comm codes....

 

Video would be good. Check what spark plugs are in there, possible the PO messed that up. Check for oil in the intake as well. For good measure you could do the 20 time brake pedal stomp (google it).

​​​​​​These types of issues come down to accurate measurement of air entering the engine and a decent ignition source. How are your long and short term fuel trims while warmed up and idling? You can look this up with your reader.

Did it have these issues during your test drive or they showed up after?

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Hey, so i'l be checking the spark plugs today. The old owner gave me 4 replacement plugs but only one of them is new and the rest are black so gonna see about cleaning them off if needed. also got some replacement coils that i might install. Yesterday i cleaned the MAF and ESS and did the 20 brake stomp. no changes to anything. Pulled the codes again and got P0301 and P0410. Still dying at idle and lagging on the acceleration. Will see if i can resolve the misfire today!

 

Ok. Make sure you have 2 leading and 2 trailing plugs. Some people get that wrong.

 

Dying at idle is often a vacuum leak that happens when the OEM intake is replaced.
Idk if the MazdaSpeed is dependable, but a lot of aftermarket intakes cause problems.

Most members will tell you the OEM intake is the best.

 

Thank you, how would i go about checking if ther's a vacuum leak? this is what;s under my hood

 

I took out the spark plugs and they seemed to be fine, just a bit of carbon build up. I cleaned them with some rubbing alcohol and a brush. The coils don't look too good though. I think I saw those "white spots" that people were talking about. Could this be the source of my problems?

 

The white spots themselves don't mean anything, but if you're not sure about the coils, change them. What you could do is get an HEI spark tester to see if they're all firing a nice strong spark. If you can ask the PO when he last changed that might help too. But net net: bad coils kill engines, and sometimes therr are no warning signs, so plan accordingly.

And they're definitely the correct plugs, in the correct positions? And they all have their ground straps?

 

Hey, the last owner told me he changed the coils, plugs and wires recently and upon inspection the plugs were find. He gave me a new set of coils though so I will change them out tomorrow and see. Also, what are g round straps?

 

Ground straps are the electrodes attached to the spark plug perimeter. Sometimes they can be knocked off.

Pictures of the spark plugs? There might be clues in their appearance.