 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Driving, Maintenance, Tuning / General Car Topics / May 2005Very Rough IDLE .. HELP!!! - 1991 Mazda MPV, 4 cyl.
BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with 240,000km/140,000 mi. It has served me very well over the yrs and I have had no real complaints with it until recently. About 6 months ago, it started developing a rough idle after warmup(idles fine when engine cold). This has become gradually worse, ...now idles very rough at around 500 RPM .. almost to the point of stalling. Here's what I've checked so far: Wires - Recently replaced but checked anyway ... consistent rhythmic blue sparks on all four Plugs- Normal Air FIlter - Replaced Rotor/Cap - Replaced O2 Sensor - Replaced PCV Valve - Replaced Air Flow Meter - Checks out, all votages within spec Idle Speed Control - Resistance within Specs Throttle Pos Sensor - Voltage within Specs Water Temp Sensor - Within spec Intake Air Tem Sensor - Within Spec Soleniod valve controlling Fuel Pressure Regualtor - checks out fine With above checks complete my attention turned to looking for either a fuel supply problem (including bad injectors), or a vacuum leak ( unmetered air entering intake manifold) Fuel Supply.... Seeing that engine runs fine at cold idle , I suspect problem is not likely with fuel delivery. Just to be sure though, I did check each injector for proper operation using a makeshift stetescope (screw driver tip on injector, ear on other end). All injectors seem to be working fine in that I could hear each of them rhythmicaly clicking away. I did not go as far as checking the fuel pressure (do not have the right tools). But seeing that cold Idle is fine, and engine can rev high without hesitation, I didn't see any point in checking.... Should I? Vacuum leak. Checked all vacuum hoses coming out of intake manifold. Pinched each one with no noticeable difference in Idle. I'm a little embarrassed to admit this part for obvious reasons...., but I also used a small propane tank (of the plumbing welding variety) and probed along all vacuum lines and all around the intake manifold..... I detected no change in idle speed at all. One final check .. the EFI self disgnostics... No codes stored.. which makes sense since engine warning light does not come on. At this point .. I'm runing out of ideas and would appreciate any suggestions out there. Needless to say, I'd rather not take it to the dealer and risk getting soaked for unnecessary expensive repairs. Thanks in advance for your responses! Regards Terry Toronto(Brampton), Ontario, Canada >BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with >240,000km/140,000 mi. It has served me very well over the yrs and I have had [quoted text clipped - 50 lines] > >Toronto(Brampton), Ontario, Canada You may have a collapsed muffler or catalytic converter. webpa Wow.. Never even thought the problem could be exhaust related... Can you explain a little more.. how the muffler or catalytic would cause the problem... only when things warm up? Can it be like an air pocket forming and thus blocking flow.. or something along those lines? Terry > >BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with > >240,000km/140,000 mi. It has served me very well over the yrs and I have had [quoted text clipped - 3 lines] > >to the point of stalling. > >........ <SNIP> > You may have a collapsed muffler or catalytic converter. > > webpa >Wow.. Never even thought the problem could be exhaust related... >Can you explain a little more.. how the muffler or catalytic would cause [quoted text clipped - 18 lines] >> >> webpa Both converter and muffler have multiple internal structures. Welds attaching these structures can corrode leaving the structures free to flop around. The exhaust system's temperature can affect this. Another poster suggested the EGR system...I thought you'd checked this. If you have...and replaced the EGR valve, did you ream-out the tubing/passageways under the valve? These can fill with carbon, thus blocking them. IIRC, a stuck-open EGR valve usually makes a poor idle. A stuck-closed EGR valve usually makes slightly worse milage and a barely noticeable high-speed roughness. webpa Hi Terry, How about the EGR system? I didn't see it listed. Maybe the symptoms you describe appear because the idle air input is being controlled by an air inlet solenoid when the engine is cold for a fast idle, which would shut off when the engine warmed up. Rough idle when warm could be a symptom of a bad EGR valve, solenoid or somesuch related component in the EGR system, where exhaust gasses are being introduced to the intake air at idle (which I think should only occur under load when warm). Just a theory, worth checking out. Matt > BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with > 240,000km/140,000 mi. It has served me very well over the yrs and I have had [quoted text clipped - 50 lines] > > Toronto(Brampton), Ontario, Canada Might be wrong.. but I think this engine uses a different type of system ... the IdleSpeedControl(ISC) which adjust idle air intake based on coolant temp... > Hi Terry, > [quoted text clipped - 65 lines] > > > > Toronto(Brampton), Ontario, Canada If you are at 500 rpm while hot it is too low usually 4 cylinders run around 700 to 1000 rpm hot idle. So this suggests insufficient air flow. One thing common is throttle body near throttle plate gets gunked up with carbon. Try disconnecting rubber boot near throttle plate. If you have a Map sensor you can get engine running and hold near 2000 rpm and have helper pulse spray carburetor cleaner around throttle plate especially into idle air inlet hole before throttle plate to get it clear. If you have a MAF sensor you usually can't keep engine running with rubber hose off so try pulling off a hose in rubber duct and with a straw on carb can and a rag around it to seal air leak a bit have helper spray into duct as you open and close throttle. If you can't keep car running disconnect rubber duct spray liberally with carb cleaner around throttle plate and idle air hole, reconnect duct, start engine and rev for a couple minutes, turn engine off and repeat process a few times. Otherwise it could be coolant temperature. but you said you checked it already. It could also be defective IAC idle air control valve that computer uses to control air flow around throttle plate. > Might be wrong.. but I think this engine uses a different type of system ... > the IdleSpeedControl(ISC) which adjust idle air intake based on coolant [quoted text clipped - 88 lines] > > > > > > Toronto(Brampton), Ontario, Canada Just going on what I know, not really familiar with this engine, but if this motor is anything like the early '90s escorts, take a look at the large air intake tube from the air box to the throttle body, if there is a large crack in it, you should be able to hold your hand over the crack and see the idle speed increase. Happened once to someone in my family, I put some duct tape on it until the part could be replaced. Matt > Might be wrong.. but I think this engine uses a different type of system ... > the IdleSpeedControl(ISC) which adjust idle air intake based on coolant [quoted text clipped - 88 lines] > > > > > > Toronto(Brampton), Ontario, Canada ok this is coming from a guy in Australia where I have had that symptom often you need to check the air flow meter now there are two types of system 1) hot wire if it is a hot wire you might find that it is still within spec but what happens is the wire becomes brittle and get's a thin coat of carbon on it this occurs from car age age i.e. the engine on and of and the fuel fumes accumulate and when the engine switches of the wire is exposed to a higher voltage so that it burns of the remains although residue is still left behind 2) air flow i.e. flap normally these system have no problem at idle as that is controlled by a screw on the side but they do carry a map sensor (manifold air pressure)now these have been know to fail to possibly to a back fire you can check these with a vacuum pump there are a few tests you can perform now what I think you could do is determine which of the two this is and go from there  SignaturePlease note that this message is intended for those named above. It may contain confidential or privileged information. If you are not the intended recipient of this message you must not use, copy, distribute or disclose it to anyone apart those named. > Just going on what I know, not really familiar with this engine, but > if this motor is anything like the early '90s escorts, take a look at [quoted text clipped - 111 lines] >> > > >> > > Toronto(Brampton), Ontario, Canada Timing belt? > BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with > 240,000km/140,000 mi. It has served me very well over the yrs and I have [quoted text clipped - 63 lines] > > Toronto(Brampton), Ontario, Canada If you just want to throw parts at it, replace the fuel filter. Throw in a bottle of HEET while you're at it. BTW, the engine light coming on has little to do with there being engine codes to check. > Timing belt? > [quoted text clipped - 65 lines] > > > > Toronto(Brampton), Ontario, Canada |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.