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Automotive/1998 malibu is idleing ruff

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Expert: - 7/12/2007


Question
I put new spark plugs and wires on my Malibu and it still idles ruff

Answer
New plugs - properly gapped and torqued in to spec, of course - and wires are fine, but clearly do not answer all problems!  Good thing to do on an engine hours rather than on an as-it-breaks - basis nonetheless.

How are your vacuum hoses?  If those are good, how are your induction system gasket interfaces?   Are they sound, or are there signs of air leaks?

The above are the very first things one should check in attempting to isolate the cause of a rough idle problem.  Rough idle generally is the result of an excessively-high air/fuel ratio, brought about by air leaks into the intake plenum, reducing the vacuum therein, a vacuum that should be at its highest at idle.  A leak can be from one (or more, depending on how much preventative maintenance you do) of a number of sources.  Common among them are deteriorated vacuum hoses, punctured vacuum actuators, and gasket interfaces which have begun to pass air as a result of relaxing hold-down bolt tension, gasket deterioration and/or warpage of what should be flat metal surfaces.

Hose and actuator problems can be isolated by opening each, one at a time, and capping off the portal from which the vacuum is taken.  If any one of these is the problem, the result of removing that circuit and capping off the feed port into the manifold should result in an immediate improvement in idle.

Of course, it could be that the problem is the collective effect of several small leaks, in which case a vacuum pump and gauge could be used to test each circuit in turn; the engine is not required to be running for this type of test.

Gasket interface tests can be found via visual inspection for dirt trails and gasket gaps, and tested via applying a drop of oil (or water, if need be) to the suspect junction.  Any leak will immediately draw the liquid in.

Emissions-testing instruments giving a high hydrocarbon (HC) reading usually also indicates a vacuum leak or leaks.

Beyond this, you may want to read up on automotive trouble-shooting and tuning techniques.  There are books available at most automotive jobbers.

Good luck ... EGK

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Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

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