I have a 95 FD with a rebuilt motor (4,000 miles ago). I recently replaced my crossover pipe with a new one. I took it for a drive and the car wouldn't boost past 5 psi and I could hear an intake piping leak. The idle became very rough and was close to stalling several times. I tightened the clamp around the crossover pipe and I can now hit 10 psi again but the idle has not improved at all. The car is constantly backfiring as well. I will also note that a week before, the engine had flooded and I replaced the plugs and did the unflood procedure and it seemed to run fine. Before this all happened, I had 18 - 20 vacuum at idle. Now I still have 18-20 vacuum until the idle stumbles (which is most of the time) and when it stumbles I only have 10 to 15 vacuum. If I rest my foot on the pedal so that the tach sits at 1,000 rpms, I have a steady 18 vacuum.

I have read several posts saying that low vacuum or fluctuating vacuum readings can be a sign of a blown engine. I just wanted to know if large vacuum fluctuations are to be expected as the idle drops down below 500 rpms. (I plan on doing a compression check when I get back in town (I'm on a 2 week business trip), so I guess I am just looking for some hope.

Any advice would be appreciated.

Raired

 

Is the plug for your air pump hooked up? If it's unplugged, or you shorted out the airpump wire and blew the fuse (it's the AC fuse in the driver's side shock tower fuse block), the car will run and idle like crap and you'll lose vacuum. Been there, done that.

Dale

 

I didn't unplug the air pump. However, I will check the fuse. Thank you very much for the advice.

 

Dale, I eliminated my air pump. My vacuum seems to be fine, but I have a PFC. Does the PFC correct this vacuum problem?

Jeremy

 

my car actually idles better when i pull the ac/airpump fuse

 

How do you take those damn relays out anyway?!?! They seem impossible to get out. Is there a certain technique?

Jeremy

 

^ are you talking about the 15a fuse?

 

have you tried to reset your ecu?

 

Sounds like a TPS problem actually, especially with the back firing. That or a ground might be loose somewhere. Believe me as funny as it sounds a few grounds and an adjustment to the TPS can make a hell of a lot of diffrence. If you dont have extra grounds installed, go out to the nearest sound shop (car stereo stuff and what not) and ask for about 8-10 feet of 4-6 gauge power wire. I got some in 4 and covered in blue. I made 7 new ones put on 5 of them (too lazy to take of UIM and alt again to get the other two, follow damiens hyper ground system set up) Car ideled like **** before hand and right after it was purring like a kitten, well a really gas kitten, but none the less purring. I would also check the seal between the elbow and throttle body for a leak maybe? And definitely adjust the TPS made my car run all funky a couple of times. Search for TPS adjustments Damien wrote upa huge thing about it. One of the other sites has it too

 

3 things:

1. Xeros may be right - TPS & grounds

2. If you had a blown engine, you would not run well at higher throttle settings.

3. Ragged idle will cause large vacuum fluctuations as the throttle plate fluctuates

 

Thank you all for your suggestions. I'll try your suggestions and get back to you!

 

The fat relays require a pair of pliers and a smooth hand to pull . You have to give enough pressure to grab the relay, but not so much that you break the relay. I typically use some channel locks.

The PFC can compensate for the missing air pump. The ECU is monitoring the O2 sensor at idle, light load, etc. and is pre-programmed to compensate for extra oxygen in the exhaust from the air pump. When it's not there, it's not sure what to do, and the car runs goofy.

I'll second checking the TPS - that's a distinct possiblity as well.

Dale

 

Ok my question with the PFC compensation has been answered. But for the FAT black relays... I just pull really hard? No tabs to release or anything? I removed my A/C relay to disable the clutch, and there was a slim tab in the front that I had to pry a little open. I don't really spot this on the relay. I.E. the MAIN relay and the EGI relay really **** me off caues i dont wanna break it .

Jeremy

 

The idle problem is fixed. I turned the screw that raises and lowers the idle until it idled at 950 rpms and it now holds 20psi of vacuum steady and idles perfectly. Also, my backfiring is gone as well. I thought the fix was going to be much more complicated but I very glad it wasn't. Thank you all for your advice.

 

"The ECU is monitoring the O2 sensor at idle, light load, etc. and is pre-programmed to compensate for extra oxygen in the exhaust from the air pump. When it's not there, it's not sure what to do, and the car runs goofy."

I have experience with only one RX-7; our 1994 FD. On my car the output of the secondary air pump is injected through a check valve directly into the catalytic converter. This is considerably downstream from the O2 sensor, and adding O2 at that point would not seem to cause the ECU to need to "compensate" for it. Can someone explain, please?

Thanks ---- Bill