Car idles extremely rough (Page 1/1)
Payson M JAN 31, 11:08 AM
Recently I put in a new engine on my Fiero as the other one had rod knock, and have had nothing but problems since. Currently, the engine has a backfire coming out of the exhaust. Starts up great off of a cold start and idles good right until it warms up. After that, the rpm will start dropping and then jumping back up again to try and keep the car going to the point where you can hear the exhaust shaking. I have gotten it to the point where it no longer will die on me but it is misfiring pretty bad still. I have stainless vacuum lines, cleaned all the injectors, and have tested fuel pressure which seems to be around 42. I have new spark wires, plugs, rotor button and cap, and various other ignition components that have been installed. Compression is also 120-130 on all cylinders. Other than that, the engine has an EGR delete plate on the bottom of the upper plenum, but the valve is still hooked up to the exhaust manifold. I am still trying to diagnose the problem and was wondering if anyone had any suggestions. Would installing a new EGR valve and EGR tube fix the issue?
fierofool JAN 31, 11:48 AM
Check your spark plug wiring. Number 1 is above the alternator. 1, 3, and 5 are trunk side cylinders. 2, is front passenger side near the battery, 4 is front center and 6 is front driver's side.

Firing order is consecutive, 1-6. Determine where you want the number 1 plug to attach to the distributor cap and mark the base of the distributor. Once you have determined that the number 1 cylinder is on the compression stroke, and the timing mark is aligned, rotate the distributor so the rotor button is pointing at the mark you made.

Then connect your plug wires in a clockwise direction in numeric order. starting with number 1 being located to align with your mark. This should put you at static timing.

With ignition off, jumper terminals A & B in your ALDL, then start the engine and rotate the distributor to set timing with a strobe light to 10-12 degrees. Turn off ignition and remove the jumper and lock down the distributor.

[This message has been edited by fierofool (edited 01-31-2025).]

82-T/A [At Work] JAN 31, 02:12 PM
I concur on the spark plugs... improper timing, or incorrect timing order (spark plug wires going to the wrong place) are almost always the cause of a really, really rough idle.
Patrick JAN 31, 03:17 PM

Long shot.. but make sure both injector fuses are good.
Payson M FEB 03, 08:27 AM
Both Injector fuses seem to be good. All timing has been set and all the wires are routed to the right cylinder. Would an EGR delete without the ECU being programmed for it cause the bouncing idle and misfire? I am also going to check valve lash and see if there are any issues there as that is something I did not check before putting the engine in.
Patrick FEB 03, 02:31 PM

quote
Originally posted by Payson M:

Both Injector fuses seem to be good.



They either are or they aren't. Don't just do a visual inspection.


quote
Originally posted by Payson M:

Would an EGR delete without the ECU being programmed for it cause the bouncing idle and misfire?



No.


quote
Originally posted by Payson M:

All timing has been set...



Have you confirmed that the outer ring of the harmonic balancer hasn't slipped? If it has slipped, the ignition timing marks are no longer valid. This is not an uncommon issue. Check by making sure #1 piston is at TDC when the widest line of the three on the balancer is at 0°. Use something like a straw in the spark plug hole of cylinder #1 while turning the crank by hand.