Engine Knock

I recently got the EGR system in my 1998 Rav4 working (replaced VSV) after driving with it non-functioning for several years. Without the system fuctioning, the engine ran great, but fuel efficiency suffered. Now, when the engine is warm only, the engine knocks and luggs between 1000 and 2000RPMs. This usually occurs right when I shift into 2nd gear. There are no engine trouble codes. Any ideas would be appreciated.


Disconnect the EGR itself for a period and see if that has any effect on the problem…

I think you have a failing EGR pressure transducer, the somewhat disc-shaped item near the EGR valve that has 3 vacuum hoses connected to it. It controls how much EGR flow there is.

Just because there are no trouble codes doesn’t mean everything is working properly.

If this is a 4 cylinder Rav4 with a manual transmission I think you ARE lugging the engine. Raise your shift point from first gear and see if it cures it.

It is almost impossible to avoid the knocking when feathering out the clutch for 2nd gear regardless of technique or shift point (within reason). 3rd is also prone to knocking , but shifting/clutch technique can minimize it. The engine runs normally until it reaches normal operating temperature. First, I will try the vacuum modulator that asemaster mentioned. Since the ERG system does not operate until the engine is warmed up, it sure seems like that is where the problem lies. Once one considers the factors of exhaust back pressure and engine vacuum on the EGR system, the problem gets more complex. My problem could could even be related to the fuel injection system ( fuel to air ratio).

Make sure all the EGR ports and passages are clear.
If the EGR is being distributed unevenly to the cylinders rough running can result.

Without the system fuctioning, the engine ran great, but fuel efficiency suffered.

I thought EFI put fuel in according to airflow measured upstream of the EGR input…I don’t see how deleting the EGR flow would mess with mixture. Theoretically, the inert gases would result in a larger throttle opening, meaning (very) slight reductions in pumping losses, but hardly something that’d stand out.

Unless “no EGR” leads to “higher combustion temps” leads to “knock” leads to “pulling off timing advance”…

The EGR transducer/modulator seems to have solved 95% of the problem. I found the OEM Denso unit new on ebay for 45$. Next I will try to thoroughly clean the EGR valve to see if I can get things working 100%.

Thanks to everyone,


Since it seems to be related to the EGR vacuum control, on my early 90’s fuel injected Corolla there’s some vacuum lines from the EGR vacuum modulator which go to the throttle body, near where the throttle plate is. The passages inside the throttle body for those are really tiny, and could conceivably get clogged up over time. If it isn’t too difficult, might be worth it to remove the throttle body for a look-see. The EGR VSV device should be considered a suspect too. The factory service manual has a procedure on how to verify its operation.