Stumbling on idle...just bouncing ideas around
 

I've got a 93 with 41.5K miles on it that i purchased last month and I'm experiencing some issues with it. I know....read the FSM. I have read it and it all looks logical, HOWEVER, I just want to see if any of the more senior members here might suggest anything else that could be causing my issues. The car is completely stock except for downpipe and K&N drop in and my problems were occurring before either of those mods. Basically, at idle after start up, the car shakes pretty bad and the idle holds steady at 750. If you give it any gas, it stumbles really bad and you can feel it struggling to build RPM. Once warm, the car idle smoothes out but still has a small miss in it. At high RPM under load, I can feel it struggling and stumbling. It's building boost but it just feels like it's cutting in and out while it's doing it.

The FSM says to look at codes (none stored), plugs (replaced), plug wires, fuel filter (replaced), air fiilter (replaced), fuel pressure, Idle Control Solenoid, and Fast Idle Cam. YES, I have checked the MAP sensor. It's not that. It doesn't shake THAT bad, but maybe about 1/3 as bad when cold. I'm thinking that more than likely the problem lies with an injector that is either stuck open or has leaking O-rings. I say this because the problem occurs when the engine is cold and at high rpm with high throttle. I have ruled out both the clutch and neutral switch because the problem exists in both neutral and/or any gear with the clutch engaged and disengaged. What does everybody else think that it might be? Thanks...just bouncing ideas around here. Will be picking up a fuel pressure gauge this week and testing to see if the system leaks down but just thinking out loud in the mean time.

loose belt? just throwing that out there i have no idea if that could be a culprit maybe someone that knows can comment on this

Check the TPS and make sure that the plug wires are good. The fuel pressure gauge is a good idea.

Unless it is flooding, I wouldn't think your problem is a leaky injector or o-ring. It sounds more like an ignition or air/fuel mixture problem - I've been wrong before though.

Have you verified that you're getting a spark on all 4 plugs?

Charlie, I just read your post and I wish I had more to offer you on yoru problem (as we're almost in the same boat here). I didn't think about the TPS. I'll check that out too.

Regarding the belts, it's not those as I replaced those as part of my routine maintenance and the problem is still there.

FYI, I had a compession test done (by puresports) and it came back at 95 psi on all 3 rotor faces both front and back.

Charlie, I still need to verify spark on all 4 plugs. That is the next thing I should do per the FSM.

would loose belts cause those same symptoms? just wondering :)

I doubt it. On these cars the belt isn't used for timing or any other major engine functions (unless you count the waterpump). Someone correct me if I'm wrong though.

-Charlie

TPS would have nothing to do with poor idle. In fact you can unplug your TPS at idle and see no difference. It only makes a difference once the throttle is pushed.

I have a similar issue on a recently (1500 miles) rebuilt (by me) engine after a 3rd gear pull to 15PSI. I have gone through everything you have plus a few more things and I am pretty sure I have a very minor seal issue on the rear rotor.

Did you notice anything different versus front and rear plugs when you changed them? My rear plugs were kinda wet and very black compared to my fronts. I was going to get a compression test done but I did a simple test and my problem was apparent.

I removed the Fuel pump relays (i have dual pumps) and unplugged my coils and removed a plug from the front rotor and then turned the cold engine over. I heard a consistant whoosh, whoosh, whoosh. Then I did the same for the rear and I heard whoosh, something different, something different, whoosh, etc. It had a loping sound that was consistant but different than the front. Sounds are hard to describe but you will hear it if you have the same problem (I hope you dont).

I will keep an eye on this thread to see what you find. Also I will let you know what I find though I wont be working on it for a few weeks as I have another FD engine rebuild to complete first before my garage is available.

Good luck,

Thanks everybody.....I'll be tearing into it this weekend and I'll let evereybody know what I find. :wallbash: Plug wires and fuel pressure gauge will be in my hands by Friday.

Just curious what's the age of your fuel how many tanks have you run through it since you bought it and is it possible there's allot of moisture in the tank ??? (sitting for awhile by previous owner or yourself ? ? ?)

I've gone through about 7 tanks since I bought it. The car had a period of about 3 years where it was primarily parked and driven about once every two months. That ended in 2004 and has been daily driven ever since then. I'll be jumping in with both feet on Friday morning and I'll keep everybody informed of what I find. I'm going to check the fuel pressure, check the spark plug wires and replace them, replace all the coolant lines (was planning on doing anyways along with thermostat,and thermoswitch). Since I'm going to have to take off the UIM to replace the wires, I'll take the throttle body off and test all the solenoids and verify that the wax rod assy is working correctly too. It will be a long weekend.

Make sure you read through the factory service manual ahead of time. A lot of the tests require the car to be running and warmed up (some of the fuel pressure tests, the wax rod test that you mentioned, double throttle, ect) - so do those before you remove the UIM.

As far as the TPS, I do think it could have negative effects on idle. Unplugging it reverts the ECU to a default setting - but if it is plugged in and sending a bad signal it will screw things up. The TPS on my Pontiac got stuck so the car thought the throttle was half way open at idle - caused high idle/idle hunting and a huge bog/hesitation when I gave it gas.

-Charlie

While you're in there, check your ignition coils as well. It's easy to do when you've got the plug wires off.


https://www.rx7club.com/3rd-generation-specific-1993-2002-16/testing-ignition-coils-spark-plug-wire-corroded-408014/

Yep....I'm going to check it all out with the car warmed up and then as I tear it down inspect it further. I'll also be checking the coils, as well as all of the solenoids on UIM.

If I see a problem with the wax rod not engaging properly, I'll use the following procedure from from FD3S.net to verify it off the car:
"The "C" point (next to last) is to line up with the roller at 76F water/engine temperature. This is adjusted with the thin screw that touches the hot wax rod shaft. The last point, "D" is suppose to disconnect(no more cold idle) at a water/engine temperature of 140F(going from memory here, please verify). This is adjusted with the large flat head screw on the back side near the double throttle area.

I had idle problems when my engine was almost warmed up, and when restarting at a temp of about 150F. All was caused by a bad hot wax rod. I replaced the unit and aligned the cam per manual. This fixed my problems.

For the 76F, I set the house AC for that measure with a digital thermometer from Radio Shack, then let the unit cool overnight. For 140F, I placed a hose and funnel to the coolant line, and poured about 2 gallons of 140F water thru it."

Thanks everybody! :)

Charlie...only one problem....I can't even SEE the frickin Fast Idle Cam mechanism / wax rod that the FSM details out. What's even worse is that I asked about half a dozen FD owners last weekend and they all pretty much pulled this number on me :scratch: :dunno: I have searched all over the net for pics of this bish and EXACTLY where it is located but haven't found any. WTF?

Ok, now I'm a bit confused. In your previous post didn't you say that you replaced your fast idle cam before? Or were you copying and pasting from someone else's post? If I remember correctly, the part is near the throttle body on the side towards the front of the car. Take a look at F-79 in the factory service manual - it shows a slightly better picture of it. I'll be back in town tomorrow afternoon and I can verify exactly where it is then.

-Charlie

Rob Robinette's website shows how to disable the fast idle cam. There are a few good photos of what it looks like:


http://robrobinette.com/throttle_body_coolant.htm

Sorry about that.....I did a cut and paste from the FD3S.net site (hence the quotes).

Turns out that I found where it is located. Had to break out the trusty mirror to see the waxrod and plunger. I could just barely see the cam from the topside. What I did notice is that the system appears to be stuck in the position corresponding to the 140F engine temp (position D on Pg F-79). I checked it with the engine cold (overnight) and the rod was stickig out and the cam was at position D. I then started the car and monitored it all through the warm up process. Rod never moved, cam never moved. I'm going to double check it again in the morning and I'll provide an update on what I find.

Thanks everybody!

so where is it then? lol i need to find mine

It's on the backside of the throttle body in between the throttle body and the firewall. You literally have to be right on top of it and looking straight down to see it (the cam). If you take a small mirror and place it on top of the oil filter, you can see the reflection of the wax rod actuator part of the system. I'll snap up some pics in the morning for you.

excellent, thanks bud!

so have you changed out the wax rod yet?

Here is a picture of the thermal waxrod unit. I din't have a good shot of the cam itself.
http://i2.photobucket.com/albums/y23...highlights.jpg

Update!!
 

Well, over the weekend I replaced all the coolant lines, the thermostat, and the thermoswitch. Upon trying to re-install the alternator, I broke the thermosensor above the thermoswitch but got a new one overnight from Malloy and solved that. I also dis-engaged the fast idle cam/wax rod assy and re-routed the throttlebody coolant lines per fd3s.net. I also checked all the sensors on the UIM/Throttlebody assy and cleaned out all the gunk and lubed it all back up. Lastly, I replaced the sparkplug wires and checked out all the ignition coils. Upon checking all the vacuum lines, I also noticed that there were 2 lines disconnected under the vacuum chamber and I plugged those back in. Topped her off with coolant last night and started it up and she purred like a kitten. No more cold start issues and a rock solid smooth idle regardless of warm or cold. I let it sit overnight and this morning I topped it off with coolant and started it back up. Smooth idle with no stumbling. Drove it work and about half-way in the idle started getting a little miss to it again. :anger: My guess is that one or both of those vacuum lines under the vacuum chamber popped back off. I'll check it tonight and provide an update.

Next stop.....fixing the apparent boost leak that I have had since I purchased the car.

The culprit...

http://www.3rdgenrx7.com/images/rebu...hippedapex.jpg

On the rear rotor. Did some minor damage on the housing.

Im glad yours was not this. :)

Did you get the boost leak fixed?

Shawn...glad to see that you found the problem. Sorry it was so far down in the engine. You have it all back together and running now?

As for my initial problem....it's still there. I re-checked all of the vacuum lines and they're all good. I know that it's not the Fast Idle Cam because I have disconnected it. Also know that it's not the Thermosensor as that has been replaced. Wires are also new. Next stop will be adjusting the TPS per Damian De LaHuerta's writeup (as it's free). After that I'll be buying a new ISC solenoid. If that doesn't work, I'm just going to bite the bullet and either take it to a reputable local rotary shop OR I'll just take the dive and replace all of the vacuum lines, check valves and upgrade to the remote solenoid system in the GB section. That'll run me $1200 total for everything though so..... :MissileSm

Unfortunately, I won't be able to do anything with the car for the next month due to a crazy schedule. :wallbash: