[Dmah9688]

I recently purchased a 1996 MX6 V6 manual transmission and I am experiencing EGR/idle issues. Since I am new to the car, I am hoping someone can help point me in the right direction.

I bought the car non-running due to a charging issue. Once I sorted that out the car ran fine for a couple months until I started experiencing coolant leaks and idle issues. Over a short period of time I had the following issues in the following order:

1. Hard starting when cold (I think this is unrelated - maybe FPR or fuel pump)
2. Intermittent rough/low idle
3. Coolant leak from back of engine evident when vehicle is shut off (drips onto exhaust/ground)

When I noticed the coolant leak I decided it was time to investigate. I could not see many sources for coolant behind the engine so I replaced the heater core hoses and the hoses to the EGR hoping that would resolve the issue. After the repair the idle was worse, the coolant leak was still present, and I started getting a P1402 error code (EGR Valve Position Sensor Circuit). When investigating the code I noticed that a previous owner had damaged the EGR position sensor connector and made a jumper using random wire and unprotected spade connectors. I tried cleaning the connections but it did not help. I attempted to remove the EGR but it is extremely difficult to access so I decided to abort since I assumed my issues were with the wiring. I got an EGR pigtail/connector from the junkyard from a Miata and bought a replacement EGR. I figured I would start with just swapping the sensor and repairing the wiring. Unfortunately, this did not fix the problem - in fact the idle is even worse, I'm getting an intermittent misfire code (P0300) and the vehicle shudders and runs poorly below 3500 rpm now.

I figure at this point I should bite the bullet and remove the EGR and inspect/replace. My concern is that previous owners have been messing around reeking havoc in this car (wiring issue above, loose intake/throttle body bolts, loose/stripped valve cover bolts, snapped bolts on the intake that control the baffle doors that I assume are part of the EGR). Basically, I don't want to go through the immense hassle of replacing the EGR if there are other diagnostic approaches I should take. Does this sound like a cut-and-dry EGR issue?

Also, maybe unrelated, but there appears to be a block-off plate on the back of the engine near the EGR but more on the passenger side of the car (I can barely see it). Does anyone know if this is stock or is this another gift from the previous owner?

It's a shame that the engine is so molested because the car is an M-edition with low mileage and a very nice interior and exterior. It ran very strong before these issues and still pulls hard above 3500 rpm. I'd keep digging on my own but every time I touch the car it seems to just get worse/develop new issues.

Thank you for your help.

 

[TwoPedalWarrior]

Welcome aboard. Fun eh? couple of intertwined issues with no clear fix. Love those.

1) Lets start with this, does the block of plate look like this KLDE EGR Valve Block Off Adapter – Welcome to King6fab
2) Car might have aftermarket headers on it, and that is often used to do the EGR delete.
3) Have you properly burped the coolant?

• turn car off
• with cool engine, pref warm, not hot, pull both rad caps off
• top of the driver side, when it starts to overflow, fill up the passenger side
• once the passenger side is topped and the driver side starts to overflow, cap the driver side
• squeeze the passenger hose to burp what you can
• start car, let run to warm up
• start topping up the passenger side, squeeze hose a bit
• you will see it burp many times, keep adding coolant until you can't really add any more due to no more bubbles
• cap it
• fill up your drivers side reservoir.
• drive for 20 minutes and look at results
• next morning, top up the last of the coolant.

4) Dizzy Cap and Rotor all can be related to a shitty idle/missfire/ crap under 3500.

Try these things and let us know

 

[Dmah9688]

Haha yeah so much fun. My usual go-to is the parts shotgun too so I might be in trouble here.

That is not what the plate looks like - I definitely have an EGR valve although this delete option intrigues me. The plate I saw is more towards the passenger side of the engine. I will see if I can snap a picture when the snow around here melts a bit and I can get under the car.

No aftermarket headers but I did replace the downpipes and exhaust (rotted out, new parts came with the car). In fact, I noticed the block-off plate when I was replacing the exhaust. I didn't think much of it at the time because the car ran fine.

As far as I can tell I bled the coolant system correctly. I'm not experiencing any overheating. When I shut the car off coolant runs down the back of the engine block and drips onto the flex pipe and boils. I imagine it happens when I am driving too but it's not noticeable then. I'm starting to think this might be an independent issue. Having replaced all of the coolant hoses behind the engine, I am starting to scratch my head on where it would be coming from.

Possibly an update on the EGR issue: The previous owner installed a cold-air intake because the factory air intake was broken somehow. Consequently, the vacuum line in the image below that says "to air intake tract" in pink was just hanging in the engine bay (anyone know if it is before or after the MAF sensor?). Not knowing what it was I put a bolt in it in case it was the source of a vacuum leak. I forgot that I did this. I just removed it and I have not had the P1402 code come back yet (admittedly, I just drove down the street and back though but before it would come on immediately the second you cleared the code). The car is still idling rough/stalling and shuddering and down on power in low rpms though. To your point, this could maybe indicate another concurrent issue (maybe distributor/spark?).

Also, the snapped bolt in the intake that I mentioned in my original post that I thought might control a baffle as part of the EGR is actually the shutter valve actuator for the VRIS 1 (see also below). This seems like another unrelated issue. Yay??? I imagine this might have some affect on low-end power but this issue predates any of the symptoms above so I don't think it is related.

Thank you for your response and help!

 

[Dmah9688]

I'm starting to wonder if the EGR code is a red herring. I can't remember if it ever came on before I incorrectly placed a bolt in the EGR vent solenoid valve hose. The sloppy wiring also added to the misdirection. For now I'm going to focus on locating and repairing the coolant leak and making sure I recalibrate the IAC and TPS correctly. Assuming I don't get any more EGR codes in the meantime, I may start broadening my search for the source of the misfire. I really don't want to go through the effort of removing the EGR unless I absolutely have to.

 

[Goodbar]

Replacing the EGR is not a big a hassle as you make it out to be, if you have time and not in a hurry. Taking off the intake manifold is easy if you have a few basic tools. From there you get access to all the hoses in the back and the EGR, so that will give you a chance to get familiar with all the hoses back there....probably will be able to have them memorized in a short period of time.

 

[Dmah9688]

That's good to hear. I hadn't looked into it too much but I was thinking I would have to access it from underneath and remove the crossmember and downpipes.

It wouldn't be a bad idea to remove and reinstall the intake and valve covers anyways since the previous owner made a mess of it.

 

[Goodbar]

A properly functioning EGR with all the hoses working seems to do wonders for the smooth performance of this car.

 

[Goodbar]

A couple of notes I remember when replacing my EGR valve:

you must have a 23 mm box wrench, it is essential to get the EGR pipe nut off the exhaust

After all was done, I thought everything was perfect, and it was for a few days. Then almost everyday I would get a code 16 and a code 29, even a code 02 sometimes. I hunted for a fix for almost 6 months. Everyday, right after start up, a code 16 and a code 29. It would go away when driving, and not be permanent. Finally one day I replaced a few of the hoses around the EGR solenoids.....and that solved it. No codes now for 2 years. The previous hoses were just not quite tight enough to prevent the codes from coming on. Only a mm size difference or so.

 

[Dmah9688]

Good to know, thanks. I don't have a 23 mm box wrench so I'll pick one up before I attempt anything.

I haven't had any time to work on the car recently so I don't really have any updates. I did try quickly pulling the vacuum line off the FPR and plugging it to check if the engine seeing full fuel pressure at lower rpms would help but I didn't notice any difference. Not sure if this would have worked even if the FPR was failing. I am still going to rent a fuel pressure diagnostic tool when I have some time. It's easy enough to check.

The weird thing is that ever since I unplugged the EGR solenoid vent that I mistakenly plugged I have gotten zero codes. The car still bucks at low rpm and idles poorly but I am not even getting a misfire code anymore which I think is odd since I assume the bucking is the engine misfiring. The bucking/sputtering immediate disappears around 2500-3000 rpm and the power comes back on like flipping a light switch. Not sure if an EGR issue/vacuum leak would behave this way or if this points to something electrical or ignition related.

At this point the car is dumping coolant out of the back of the engine (btw the engine and the firewall) anyways so I can no longer ignore it. I'm running out of places the coolant can be coming from. I've never seen a head gasket pour coolant out externally but I'm starting to worry this might be the issue. At least it's leaking so much that the problem should be pretty obvious once I finally have time to climb back under it.

Also, I hate to do it since they look okay but I am going to replace the spark plugs and wires as a hail mary.

 

[fredtw0]

At 250k miles, I had an oil leak through the shaft of the distributor. That caused the disty to short out randomly.
In have seen the crankshaft position sensor go funky when coolant is spilled on the connector.
Also vacuum leaks can occur where the intake and head surfaces meet. Might get new gaskets and get that sealed.
Also check small coolant lines feeding egr and throttle body. Both ends of each should have clamps (easier to get to with intake removal)
Biggest annoyance with the intake is all the hoses and vacuum lines. And the 96 has the most.

 

[Dmah9688]

Oh okay thanks, that gives me a couple other places to look if I strike out on the EGR/vacuum issues.

Yeah, at this point I don't think I have a choice but to replace the intake manifold gasket. Everything the previous owner touched got messed up and I know he removed the intake at one point.

I have replaced the coolant hoses to the EGR, throttle body, and heater core because they all showed signs of degradation. That's what has me a little nervous because there is not much else back there that should leak coolant (maybe a freeze plug?). I just need to stop being lazy and make the time to climb under the car though as it "should" be obvious from underneath.

 

[fredtw0]

Oh right, and that more circular plate may be the factory position for a block heater. Cant find them anymore, but they did exist and bolted in back there. As such, it acts as a freeze plug and may be leaky if somebody removed it before.

Oh... And if you do remove the intake, and if you aim to have the EGR operational, you might clean the in-head channel. The EGR glasses flow through the valve, through the head, through the intake, and comes out near the throttle body, if I recall correctly.

If somebody was mucking around, might check that the TB to intake elbow is intact.

 

[Dmah9688]

Okay great, thanks, I appreciate the info. Do you know if anyone still sells the elbow on the intake? Mine is suspect and I'm not sure it is fully sealing after I removed and reinstalled it. My idle is hunting a bit on top of just being crappy in general.

I snuck out of work early and climbed under the car. The coolant leak appears to be coming from the one heater hose coming out of the intake that I did not replace because it does not run behind the engine. The coolant runs down the block and ends up dripping behind the engine though.

It appears the block-off plate I was talking about is factory (see circled stock photo). Not sure what it's for but I'm not going to worry about it.

 

[fredtw0]

Yeah, that's the block heater block off plate.

Idk about the elbow.... I could look and see if I have one. Doubtful.

 

[Dmah9688]

That would be awesome, thanks. Don't spend too much time looking though, I am sure I can make something else work if need be. I could probably just get away with using some hose clamps in place of the factory clamps. I don't think the hose is torn, it just doesn't seem to seat well.

I just replaced the spark plug and wires and it seems like it did help a bit. I'll have a better idea once I fix the coolant leak and can drive the car longer distances. The good news is the old plugs all looked great. The bad news is that they appear to be new iridium NGKs that I just replaced with cheap-o copper plugs. Same with the spark plug wires; replaced nice NGKs with a cheap set from Rockauto. I've been slandering the previous owners but they had deeper pockets than me, anyways.

At this point there's nothing left to do but fix the coolant leak and do a deep dive on the intake and replace all worn gaskets/hoses. I'll report back with my results once I have time to do the job.

 

[Goodbar]

I did buy a replacement elbow a while back, so likely they are still for sale. I may have an extra one among my parts. And the hose connection that comes off the elbow is very important to not have an air leak. The car will run poorly if the connection there is not sealed well.

Hope the leak around the heater hose is the hose, and not the heater core. If it is the heater core you should find some dampness on the passenger side floor or around there.

I had cheap spark plug wires for a while, replaced them with NGK blue wires, and the car runs a lot better.....although the previous cheap plug wires did work okay for quite a while.

 

[Dmah9688]

Luckily, the leak is not from the heater core. That was the first place I checked when the leak started. It's just a weeping hose from one of the hoses coming off of the intake on the transmission side of the engine. Should be an easy repair.

Yeah I might go back to the NGK wires if the problem is still present with the new wires as the quality of the NGKs is significantly better than the cheap set I bought. I'm not so worried about the plugs as copper plugs work really well they just don't last as long.