I'm in the process of tracking down a sudden change in my cold idle, and I'd really appreciate any opinions from the experts. 1991 348, 35,000 miles, with a fresh (6 month) major from a very qualified independent. Car ran beautifully, only issue was the occasional Slow Down 5/8 and a 1211 (Lamba issue- fuel/air problem). CEL had no apparent impact on performance, and if cleared, would not reappear for 100 miles or more. Water pump was also replaced during major. After a few weeks I noticed that the car was running about 15 degrees cooler. Dropping down to 176 or so while cruising. Prior to major it hung out at 195. Assuming this was causing extra enrichment and my errant CEL 5/8, I replaced thermostat. Confirmed the old thermostat was not opening per workshop manual spec. Car began running in proper temp range, but no change in random CEL. Changed O2 sensor with Bosch universals. No change either. Car is still running beautifully. CEL is very intermittent. No loss of power, great idle, starts fine everytime. Exhaust is replaced and test pipes put in for cats. Cat ECU's disconnected. Car still running great. Sounds magical! Here is where it gets weird. While replacing my stereo, I cleaned some contacts and tightened up some grounds behind the passenger footwell fusebox. I also replaced the A/C fuse in the trunk with an equally rated breaker. After returning power to the car and beginning an ECU idle learn process, the car suddenly was running really rough at idle. Loping like a muscle car with a big cam, some quiet popping in the exhaust. As soon as the air injection ended, however, the car sounded fine again. I tried the idle learn several times, and checked the fusebox again, assuming I knocked something loose. Same thing. Car runs great warm, but when cold, loping, surging idle, and hesitation/stumbling at low RPMs. I also noticed that my once erratic and rare CEL 5/8 1211 Lamba error was now flickering on and off, even at idle. It would not stay on, but was definitely more present. When the throttle was depressed, the CEL would turn off. The only changes that preceded this idle problem were in the fuse box area. It wasn't like the car was run hard prior, missed a shift, etc. It started and ran perfectly when pulled into the garage for the wiring, then a few hours later, lumpy cam idle. After this, I began a systematic diagnosis. While it was improbable that some other system just happened to fail, unrelated to my stereo work, I couldn't discount the possibility any longer. Below is the list of things I've done since. I realize some of these aren't related, but I saw this as an opportunity to do some preventative maintenance as well: - Checked both ECU harness for appropriate resistance and voltage of all systems, except ones when the car was running. - Cleaned IACV. Seemed to actuate fine. Both buzz when key is on. - Replaced relays for fuel pumps and ignition systems. - Checked all plugs. None seemed fouled. Middle 2 on 5/8 bank may have been slightly whiter than others? - Cleaned grounds throughout the car. - Opened and re-flowed solder in the entire fusebox. - Checked resistance on MAFs. Cleaned them with MAF cleaner. - Checked TPS on both sides. Not perfect, but very close to spec on both sides. - Removed and cleaned idle air adjustment screws. Significant build up on these. - Swapped left and right O2 sensors. - Swapped temp sensors. Checked harness and resistance, but not voltage. - Cleaned two way valve. - Cleaned contacts on buss bar behind fuse box. - Cleaned and adjusted contacts on coil, power module, and all other engine sensors. - Inspected crank sensors and harness. - Checked harness on cam sensor. Was replaced about 4 years ago. Did not check sensor. - Replaced battery. Old one at full charge was about 12.3v. Not terrible but likely on its way out. After all this, I fixed several issues I've had for a long time (light in the glove box, for example) but the loping and weak, cold idle remained. The car doesn't want to stall, but it seems to be surging more than usual, and still the biggest oddity is the hesitation from about 1000 to 2200 RPM. Once warm, it all goes away and it purrs. In fact, it runs better warm now then it did before! On one test drive the idle did seem to stick around 1,500 a few times, but I lubricated the throttle linkage and that seems to have been fixed. Can't guarantee it was related, but I wanted to mention it. Tonight I pulled the O2 sensors to see what it would do in open loop. Still had a lopey cold idle. Pulled the vacuum lines off the cut off valves and noticed that it smoothed out a noticeable amount. I also noticed that when I covered the vacuum line I removed from the 5/8 side cutoff, I could hear what sounded like the air injection system start running in the top air intake on the driver side. Curiously, if I put my finger on the 1/4 side, I do NOT hear the "gurgling" sound in the air intake. First time I've found some variance between sides! Despite the engine reaching 195 F, I could still put my finger on the 5/8 vacuum line (with the valve disconnected) and hear the noise in the intake. Now I'm wondering if there is a fuel issue? But if so, wouldn't I have issues at higher RPMs? Leaking injector maybe? After reattaching the O2 sensors and starting the car again, the 5/8 side immediately stopped making the noise regardless of whether I had the vacuum line covered, attached, or loose. So this leads me to my current mystery. What could have made the idle change, and why does covering the check valve vacuum line on one side (when the O2 is disconnected) cause the air injection system to keep running on 5/8, but not 1/4? Based on the fact that this only happens when cold, I'm sure that this is some sort of emission system that has failed, maybe the electrovalve, but I'd sure appreciate any insight that you may have. I'm not opposed to taking it to a pro for diagnosis, as I'm sure my mechanic and an SD1 could find the issue quickly, but honestly, I enjoy tracking this down and learning about the vehicle. Thanks!
Wow certainly being thorough. Did you check alternator voltage, sometimes this can cause issues. Also check to make sure ground connections are ok. The only reason for this is all the electrical stuff you have already checked, these two items seem to all that is left baring injectors, and control modules. Is the fuel filter clean or partially blocked? Or fuel pumps ok? The reason I suggest this is when cold the FI will run in open circuit, ie does not correct for air fuel ratio, when up to temp will go closed circuit and can correct for minor variations. Good luck with it.
Can you take a picture of this Cut Off Valve? How was the idle when "Despite the engine reaching 195 F, I could still put my finger on the 5/8 vacuum line (with the valve disconnected) and hear the noise in the intake" was happening?
I've been through every ground I can find, so much so that I plan on making a ground location list for sharing. Ignition and fuel are still areas to explore, with fuel being my chief suspect at this point. I'm almost wondering if something I fixed in the fuse box is simply exacerbating a long running fuel issue? Traveling today, but I may pick up a fuel pressure gauge to test with. On that note, any idea what fittings I need?
When the air pump (or whatever generates that burble) was engaged, the loping idle appeared. When I left the vacuum line open, the pump stopped and the idle smoothed out considerably. Too much air and maybe not enough fuel? Maybe enrichment is too lean for the default air mixture?
Small white valve that is vacuum actuated that feeds air from the air box to the emission system ( I think?). It has two big black air lines and one small line from the intake manifold. Located on either side. Will try to find a pic when I can. Number 8 in pic I found. Best I can find on my phone. Image Unavailable, Please Login
Yes that is the vacuum actuated switch that controls the feeding of the cool air into the exhaust stream at start up to burn off the rich condition. If you are having problem with that, change the two one way valve item 4 on that picture. They can be bought for cheap from Pepboys. And if that does not work then change the switches.
+1 In addition to what Mitchell said.......... And totally guessing here, You may want to look into replacing the intake gaskets between the plenum and runners, as well as the gaskets between the heads and runners. If you are getting extra air into the engine after the MAFs it will cause a lean condition that the O2 sensors will pick up on. Then the ECU/s will try to adjust the fuel trim. The ecu/s will also see the air coming in from the mafs and then try to adjust the trim again. So if you have a leaky intake that can cause erratic issues. The hunting idle could also be because of a leaking intake/hose. The ECUs could see a high idle and adjust the iacv. But because of possible extra air leaking past the intake can cause the idle to raise again. Up and down, up and down, because of an intake leak. I had this issue on my old Integra because of a busted vacuum tube. Then on my BMW because of a broken intake compensation valve. Then on my Expedition because of a broken EGR hose. The ECUs do NOT like air that they cannot account for. Also have a look at the oil vapor hoses attached to the bottom of the intake tubes, just before they connect to the throttle bodies. Maybe one could have popped out???? My guess as to why it goes away when warm is because, things expand as they heat up, thus the possible leak gets sealed up????? I would start by making sure all the nuts attaching the plenum to the runners are properly tightened, and then check to make sure the bolts attaching the intake to the heads are properly tightened. Or as Mitchell suggested, the check valves are shot, and once the ecu stops the secondary air injection the engine isn't getting the extra hot air. It wouldn't be a bad idea to send out your injectors to get tested and cleaned. Here's is the how-to for the injectors and intake remove (should you need to remove the intake). http://www.ferrarichat.com/forum/technical-q/305475-348-fuel-injector-intake-plenum-removal.html you said that two of your plugs were a bit white, which indicates a lean condition. So you may have some gummed up injectors???? Then I would consider doing this: http://www.ferrarichat.com/forum/technical-q/444155-348-motronic-2-7-connector-harness-repin-2.html#post143057320 And this: http://www.ferrarichat.com/forum/technical-q/351819-348-ecu-removal-chip-removal.html Those are my Stooge guesses.
I had the same erratic idle and stall issue. I had just completed a major major where i had the entire upper engine apart and literally took painstaking effort to put together the cleanest 348 you'll ever see. Every component was either new or diagnosed as perfect. No vacuum leaks as well. I had noticed once that by simply touching the secondary air intake tube assembly that the engine idle would change suddenly. But hell, that of course could not make sense since that system has nothing to do with idle vacuums in any way, its simply not in the loop. But today, after the problem became so bad that the car would stall at every corner I had to stare at it for a while and think. While staring at that stupid secondary tube I noticed a interesting thing .... the MAV cable is literally resting on the secondary tube. In other words when I was moving about the secondary tube I was also jiggling the MAV cable. So ... even though the MAV connector pins looked clean, I used some contact cleaner on them and re-connected diligently. The world change.
Make sure the throttle posisjon sensor is correctly set and adjusted. The varying rpms. is like that because the idle air control elektromagnetic valve try to compensate for something. If the the throttle is not at zero, the idle control valve is not working normally. So when the rpms. gets really low, it try to compensate by opening and prohibiting the engine to stall. If the ecu thinks you have 10% throttle, it disable the idle mode. I had that problem on a Maserati biturbo with fuel injection. Just made half a turn out on the throttle butterfly screw so the engine ecu understood that the throttle was at zero and then the idle air control worked perfectly. I am not saying that this is the problem with your car, but it could be. Good luck. Erik
