420 SEL idle surge

[Carlo(s)]

After new timing chain + rails + new oil + filter & valve seals car was idling smooth and had good power for about 20 miles; filled tank with regular gas and a slight rough idle appeared that is getting rougher and engine is down in power; car surges 300 RPM up and down at idle; no starting problems hot or cold; all plug wires cap & rotor new in the last 10,000 miles; checked all Bosch Wd9 Super R plugs that have a about 20,000 miles and all have strong spark, cleaned them out and re-gapped at .42 to no avail. Fuel filter is about a year old; new bosch fuel pumps within last year new injectors and injector seals + air distribution tube. Any suggestions would be appreciated.

[Tims450SL]

a for sale sign maybe?

[david s poole]

try using super unleaded [which i think is specified for that engine]

[Carlo(s)]

Thanks Dave.. I found a large vacuum line that originates at the air pump disconnected and sitting behind the water pump; can you shed some light where this vacuum line connects to?

[alexcooper87]

it goes to the intake behind the air valve down low on driver side of intake long needle nose and flash light and lots of yelling its a pain in the a** good luck

[Carlo(s)]

Update: changed clogged fuel filter (had lots of mud and black soot in it) and engine idle returned to very smooth and power back to normal; still fell small idle surge which may be cured once the air pump vacuum hose is connected. Any photo of where it is under the manifold behind the air valve that can help me pinpoint it location?

[79Mercy]

You also may have a leaking intake manifold gasket.